diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/ArffLoader.java b/samoa-instances/src/main/java/org/apache/samoa/instances/ArffLoader.java
index dd82eda..51f5893 100644
--- a/samoa-instances/src/main/java/org/apache/samoa/instances/ArffLoader.java
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/ArffLoader.java
@@ -29,6 +29,9 @@
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
+/**
+ * The Class ArffLoader. Loads an Arff file with sparse or dense format.
+ */
 public class ArffLoader implements Loader {
 
   /**
@@ -42,12 +45,14 @@
    * The stream tokenizer.
    */
   protected transient StreamTokenizer streamTokenizer;
+  protected Range range;
+  protected List<Attribute> auxAttributes;
 
   /**
    * Instantiates a new arff loader.
    *
-   * @param reader the reader
-   * @param size the size
+   * @param reader         the reader
+   * @param size           the size
    * @param classAttribute the class attribute
    */
   public ArffLoader(Reader reader, int size, int classAttribute) {
@@ -61,8 +66,6 @@
     }
   }
 
-  protected Range range;
-
   /**
    * Instantiates a new arff loader.
    *
@@ -169,7 +172,7 @@
       while (numAttribute == 0 && streamTokenizer.ttype != StreamTokenizer.TT_EOF) {
         //For each line
         while (streamTokenizer.ttype != StreamTokenizer.TT_EOL
-            && streamTokenizer.ttype != StreamTokenizer.TT_EOF) {
+                && streamTokenizer.ttype != StreamTokenizer.TT_EOF) {
           //For each item
           if (streamTokenizer.ttype == StreamTokenizer.TT_NUMBER) {
             //System.out.println(streamTokenizer.nval + "Num ");
@@ -177,7 +180,7 @@
             ++numAttribute;
 
           } else if (streamTokenizer.sval != null && (streamTokenizer.ttype == StreamTokenizer.TT_WORD
-              || streamTokenizer.ttype == 34 || streamTokenizer.ttype == 39)) {
+                  || streamTokenizer.ttype == 34 || streamTokenizer.ttype == 39)) {
             //System.out.println(streamTokenizer.sval + "Str");
             boolean isNumeric = this.auxAttributes.get(numAttribute).isNumeric();
             double value;
@@ -189,7 +192,7 @@
               value = this.auxAttributes.get(numAttribute).indexOfValue(streamTokenizer.sval);
             }
 
-            instance.setValue(numAttribute,value);//this.setValue(instance, numAttribute, value, isNumeric);
+            instance.setValue(numAttribute, value);//this.setValue(instance, numAttribute, value, isNumeric);
             ++numAttribute;
           }
           streamTokenizer.nextToken();
@@ -242,7 +245,7 @@
       streamTokenizer.nextToken(); // Remove the '{' char
       //For each line
       while (streamTokenizer.ttype != StreamTokenizer.TT_EOL
-          && streamTokenizer.ttype != StreamTokenizer.TT_EOF) {
+              && streamTokenizer.ttype != StreamTokenizer.TT_EOF) {
         while (streamTokenizer.ttype != '}') {
           //For each item
           //streamTokenizer.nextToken();
@@ -262,7 +265,7 @@
             //numAttribute++;
 
           } else if (streamTokenizer.sval != null && (streamTokenizer.ttype == StreamTokenizer.TT_WORD
-              || streamTokenizer.ttype == 34 || streamTokenizer.ttype == 39)) {
+                  || streamTokenizer.ttype == 34 || streamTokenizer.ttype == 39)) {
             //System.out.print(streamTokenizer.sval + "-");
             if (this.auxAttributes.get(numAttribute).isNumeric()) {
               this.setSparseValue(instance, indexValues, attributeValues, numAttribute, Double.valueOf(streamTokenizer.sval).doubleValue(), true);
@@ -309,6 +312,9 @@
     //System.out.println(numAttribute+":"+valueAttribute+","+this.instanceInformation.classIndex()+","+value);
   }
 
+  //protected List<Attribute> inputAttributes;
+  // protected List<Attribute> outputAttributes;
+
   /**
    * Reads an instance sparse and returns a dense one.
    *
@@ -324,7 +330,7 @@
       streamTokenizer.nextToken(); // Remove the '{' char
       //For each line
       while (streamTokenizer.ttype != StreamTokenizer.TT_EOL
-          && streamTokenizer.ttype != StreamTokenizer.TT_EOF) {
+              && streamTokenizer.ttype != StreamTokenizer.TT_EOF) {
         while (streamTokenizer.ttype != '}') {
           //For each item
           //streamTokenizer.nextToken();
@@ -339,7 +345,7 @@
             //numAttribute++;
 
           } else if (streamTokenizer.sval != null && (streamTokenizer.ttype == StreamTokenizer.TT_WORD
-              || streamTokenizer.ttype == 34)) {
+                  || streamTokenizer.ttype == 34)) {
             //System.out.print(streamTokenizer.sval + "/"+this.auxAttributes.get(numAttribute).indexOfValue(streamTokenizer.sval)+" ");
             if (this.auxAttributes.get(numAttribute).isNumeric()) {
               instance.setValue(numAttribute, Double.valueOf(streamTokenizer.sval).doubleValue());//this.setValue(instance, numAttribute, Double.valueOf(streamTokenizer.sval).doubleValue(), true);
@@ -362,11 +368,6 @@
     return instance;
   }
 
-  //protected List<Attribute> inputAttributes;
-  // protected List<Attribute> outputAttributes;
-
-  protected List<Attribute> auxAttributes;
-
   private InstanceInformation getHeader() {
     //commented JD
     //this.range.setUpper(10000); //TO DO: Create a new range object with isInRange that does not need the upper limit
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/Attribute.java b/samoa-instances/src/main/java/org/apache/samoa/instances/Attribute.java
index 4f49b43..ff9a529 100644
--- a/samoa-instances/src/main/java/org/apache/samoa/instances/Attribute.java
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/Attribute.java
@@ -24,6 +24,9 @@
 import java.text.SimpleDateFormat;
 import java.util.*;
 
+/**
+ * Class that keeps all information needed to describe a feature or attribute.
+ */
 public class Attribute implements Serializable {
 
   /** The keyword used to denote the start of an arff attribute declaration */
@@ -68,8 +71,8 @@
    */
   protected boolean isDate;
 
-  /** 
-   * Date format specification for date attributes 
+  /**
+   * Date format specification for date attributes
    */
   protected SimpleDateFormat m_DateFormat;
 
@@ -122,7 +125,7 @@
    * @param dateFormat the format of the date used
    */
   public Attribute(String attributeName, String dateFormat) {
-    this.name = attributeName;        
+    this.name = attributeName;
     this.valuesStringAttribute = null;
     this.isDate = true;
 
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/AttributesInformation.java b/samoa-instances/src/main/java/org/apache/samoa/instances/AttributesInformation.java
index 214a716..a3b2c52 100644
--- a/samoa-instances/src/main/java/org/apache/samoa/instances/AttributesInformation.java
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/AttributesInformation.java
@@ -24,13 +24,19 @@
 import java.util.ArrayList;
 import java.util.List;
 
+/**
+ * Class for storing the information of the attributes.
+ * It stores only information about discrete attributes and suppose that
+ * the default attribute is numeric.
+ */
 public class AttributesInformation implements Serializable {
 
   /**
    * The attribute information.
    */
-  protected List<Attribute> attributes;
-  protected List<Integer> indexValues;
+  protected Attribute[] attributes;
+
+  protected int[] indexValues;
   /**
    * The number of attributes.
    */
@@ -42,22 +48,32 @@
   protected Attribute defaultNumericAttribute;
 
   public AttributesInformation(AttributesInformation chunk) {
-    this.attributes = chunk.attributes;
-    this.indexValues = chunk.indexValues;
+    this.attributes = chunk.attributes.clone();
+    this.indexValues = chunk.indexValues.clone();
     this.numberAttributes = chunk.numberAttributes;
   }
 
-  public AttributesInformation(List<Attribute> v, List<Integer> i, int numberAttributes) {
+  public AttributesInformation(Attribute[] v, int[] i, int numberAttributes) {
     this.attributes = v;
     this.indexValues = i;
     this.numberAttributes = numberAttributes;
   }
 
-  public AttributesInformation(List<Attribute> v, int numberAttributes) {
+  public AttributesInformation(Attribute[] v, int numberAttributes) {
     this.attributes = v;
-    this.indexValues = new ArrayList<Integer>(numberAttributes);
+    this.indexValues = new int[numberAttributes];
     for (int i = 0; i < numberAttributes; i++) {
-      this.indexValues.add(i);
+      this.indexValues[i] = i;
+    }
+    this.numberAttributes = numberAttributes;
+  }
+
+  public AttributesInformation(List<Attribute> v, int numberAttributes) {
+    this.attributes = new Attribute[numberAttributes];
+    this.indexValues = new int[numberAttributes];
+    for (int i = 0; i < numberAttributes; i++) {
+      this.indexValues[i] = i;
+      this.attributes[i] = v.get(i);
     }
     this.numberAttributes = numberAttributes;
   }
@@ -85,22 +101,26 @@
       //if there is not attribute information, it is numeric
       return defaultNumericAttribute();
     }
-    return attributes.get(location);
+    return attributes[location];
   }
 
-  public void add(Attribute attribute, int value) {
-    this.attributes.add(attribute);
-    this.indexValues.add(value);
-  }
+  /*public void add(Attribute attribute, int value) {
+      this.attributes.add(attribute);
+      this.indexValues.add(value);
+  }*/
 
   /**
    * Sets the attribute information.
    *
    * @param v the new attribute information
    */
-  public void setAttributes(List<Attribute> v) {
+  public void setAttributes(Attribute[] v) {
     this.attributes = v;
-    this.numberAttributes=v.size();
+    this.numberAttributes = v.length;
+    this.indexValues = new int[numberAttributes];
+    for (int i = 0; i < numberAttributes; i++) {
+      this.indexValues[i] = i;
+    }
   }
 
   /**
@@ -112,24 +132,24 @@
   public int locateIndex(int index) {
 
     int min = 0;
-    int max = this.indexValues.size() - 1;
+    int max = this.indexValues.length - 1;
 
     if (max == -1) {
       return -1;
     }
 
     // Binary search
-    while ((this.indexValues.get(min) <= index) && (this.indexValues.get(max) >= index)) {
+    while ((this.indexValues[min] <= index) && (this.indexValues[max] >= index)) {
       int current = (max + min) / 2;
-      if (this.indexValues.get(current) > index) {
+      if (this.indexValues[current] > index) {
         max = current - 1;
-      } else if (this.indexValues.get(current) < index) {
+      } else if (this.indexValues[current] < index) {
         min = current + 1;
       } else {
         return current;
       }
     }
-    if (this.indexValues.get(max) < index) {
+    if (this.indexValues[max] < index) {
       return max;
     } else {
       return min - 1;
@@ -143,47 +163,77 @@
     return this.defaultNumericAttribute;
   }
 
-  public void setAttributes(List<Attribute> v, List<Integer> indexValues) {
+  public void setAttributes(Attribute[] v, int[] indexValues) {
     this.attributes = v;
-    this.numberAttributes=v.size();	
-    this.indexValues=indexValues;
+    this.numberAttributes = v.length;
+    this.indexValues = indexValues;
   }
-  
-  public void deleteAttributeAt(Integer position) {
-        if ((position < 0) || (position >= attributes.size())) {
-            throw new IllegalArgumentException("Index out of range");
-        }
 
-        ArrayList<Attribute> newList = new ArrayList<Attribute>(attributes.size() - 1);
-        for (int i = 0 ; i < position; i++) {
-            Attribute att = attributes.get(i);
-            newList.add(att);
-        }
-        for (int i = position + 1; i < attributes.size(); i++) {
-            Attribute newAtt = (Attribute) attributes.get(i);
-            newList.add(newAtt);
-        }
-        attributes = newList;
+  public void deleteAttributeAt(int position) {
+
+    int index = locateIndex(position);
+
+    this.numberAttributes--;
+    if ((index >= 0) && (indexValues[index] == position)) {
+      int[] tempIndices = new int[indexValues.length - 1];
+      Attribute[] tempValues = new Attribute[attributes.length - 1];
+      System.arraycopy(indexValues, 0, tempIndices, 0, index);
+      System.arraycopy(attributes, 0, tempValues, 0, index);
+      for (int i = index; i < indexValues.length - 1; i++) {
+        tempIndices[i] = indexValues[i + 1] - 1;
+        tempValues[i] = attributes[i + 1];
+      }
+      indexValues = tempIndices;
+      attributes = tempValues;
+    } else {
+      int[] tempIndices = new int[indexValues.length];
+      Attribute[] tempValues = new Attribute[attributes.length];
+      System.arraycopy(indexValues, 0, tempIndices, 0, index + 1);
+      System.arraycopy(attributes, 0, tempValues, 0, index + 1);
+      for (int i = index + 1; i < indexValues.length; i++) {
+        tempIndices[i] = indexValues[i] - 1;
+        tempValues[i] = attributes[i];
+      }
+      indexValues = tempIndices;
+      attributes = tempValues;
     }
+  }
 
-    public void insertAttributeAt(Attribute att, int position) {
-
-        if ((position < 0) || (position > attributes.size())) {
-            throw new IllegalArgumentException("Index out of range");
-        }
-
-        ArrayList<Attribute> newList = new ArrayList<Attribute>(attributes.size() + 1);
-        for (int i = 0 ; i < position; i++) {
-            Attribute oldAtt = attributes.get(i);
-            newList.add(oldAtt);
-        }
-        newList.add(att);
-        for (int i = position; i < attributes.size(); i++) {
-            Attribute newAtt = (Attribute) attributes.get(i);
-            newList.add(newAtt);
-        }
-        attributes = newList;
-
+  public void insertAttributeAt(Attribute attribute, int position) {
+    if ((position < 0) || (position > this.numberAttributes)) {
+      throw new IllegalArgumentException("Can't insert attribute: index out "
+              + "of range");
     }
+    int index = locateIndex(position);
+
+    this.numberAttributes++;
+    if ((index >= 0) && (indexValues[index] == position)) {
+      int[] tempIndices = new int[indexValues.length + 1];
+      Attribute[] tempValues = new Attribute[attributes.length + 1];
+      System.arraycopy(indexValues, 0, tempIndices, 0, index);
+      System.arraycopy(attributes, 0, tempValues, 0, index);
+      tempIndices[index] = position;
+      tempValues[index] = attribute;
+      for (int i = index; i < indexValues.length; i++) {
+        tempIndices[i + 1] = indexValues[i] + 1;
+        tempValues[i + 1] = attributes[i];
+      }
+      indexValues = tempIndices;
+      attributes = tempValues;
+    } else {
+      int[] tempIndices = new int[indexValues.length + 1];
+      Attribute[] tempValues = new Attribute[attributes.length + 1];
+      System.arraycopy(indexValues, 0, tempIndices, 0, index + 1);
+      System.arraycopy(attributes, 0, tempValues, 0, index + 1);
+      tempIndices[index + 1] = position;
+      tempValues[index + 1] = attribute;
+      for (int i = index + 1; i < indexValues.length; i++) {
+        tempIndices[i + 1] = indexValues[i] + 1;
+        tempValues[i + 1] = attributes[i];
+      }
+      indexValues = tempIndices;
+      attributes = tempValues;
+    }
+  }
 
 }
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/DenseInstance.java b/samoa-instances/src/main/java/org/apache/samoa/instances/DenseInstance.java
index d8a789b..30652f3 100644
--- a/samoa-instances/src/main/java/org/apache/samoa/instances/DenseInstance.java
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/DenseInstance.java
@@ -20,6 +20,9 @@
  * #L%
  */
 
+ /**
+ * Class that stores an instance that uses a dense representation.
+ */
 public class DenseInstance extends InstanceImpl {
 
   /**
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/FilteredSparseInstance.java b/samoa-instances/src/main/java/org/apache/samoa/instances/FilteredSparseInstance.java
new file mode 100644
index 0000000..a762b79
--- /dev/null
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/FilteredSparseInstance.java
@@ -0,0 +1,80 @@
+package org.apache.samoa.instances;
+
+/*
+ * #%L
+ * SAMOA
+ * %%
+ * Copyright (C) 2014 - 2015 Apache Software Foundation
+ * %%
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * #L%
+ */
+
+/**
+ * The Class FilteredSparseInstance.
+ * <p>
+ * This class is an extension to the original SparseInstance.
+ * It has been created to be used with feature selection
+ * algorithms for data streams.
+ * In contrast to SparseInstance objects, missing values are
+ * represented as NaNs instead of 0s (zeros).
+ * This allows learners to skip features with missing values.
+ *
+ * @author Jean Paul Barddal
+ */
+public class FilteredSparseInstance extends SparseInstance {
+
+  /**
+   * Instantiates a new sparse instance.
+   *
+   * @param d   the d
+   * @param res the res
+   */
+  public FilteredSparseInstance(double d, double[] res) {
+    super(d, res);
+  }
+
+
+  /**
+   * Instantiates a new sparse instance.
+   *
+   * @param inst the inst
+   */
+  public FilteredSparseInstance(InstanceImpl inst) {
+    super(inst);
+  }
+
+  /**
+   * Instantiates a new sparse instance.
+   *
+   * @param numberAttributes the number attributes
+   */
+  public FilteredSparseInstance(double numberAttributes) {
+    super(numberAttributes);
+  }
+
+  /**
+   * Instantiates a new sparse instance.
+   *
+   * @param weight           the weight
+   * @param attributeValues  the attribute values
+   * @param indexValues      the index values
+   * @param numberAttributes the number attributes
+   */
+  public FilteredSparseInstance(double weight, double[] attributeValues, int[] indexValues, int numberAttributes) {
+    super(numberAttributes);
+    this.weight = weight;
+    this.instanceData = new FilteredSparseInstanceData(attributeValues, indexValues, numberAttributes);
+  }
+
+}
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/FilteredSparseInstanceData.java b/samoa-instances/src/main/java/org/apache/samoa/instances/FilteredSparseInstanceData.java
new file mode 100644
index 0000000..d1d4848
--- /dev/null
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/FilteredSparseInstanceData.java
@@ -0,0 +1,68 @@
+package org.apache.samoa.instances;
+
+/*
+ * #%L
+ * SAMOA
+ * %%
+ * Copyright (C) 2014 - 2015 Apache Software Foundation
+ * %%
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * #L%
+ */
+
+/**
+ * The Class FilteredSparseInstanceData.
+ * <p>
+ * This class is an extension to the original SparseInstanceData.
+ * It has been created to be used with feature selection
+ * algorithms for data streams.
+ * In contrast to SparseInstanceData objects, missing values are
+ * represented as NaNs instead of 0s (zeros).
+ * This allows learners to skip features with missing values.
+ *
+ * @author Jean Paul Barddal
+ */
+public class FilteredSparseInstanceData extends SparseInstanceData {
+
+
+  /**
+   * Instantiates a new sparse instance data.
+   *
+   * @param attributeValues  the attribute values
+   * @param indexValues      the index values
+   * @param numberAttributes the number attributes
+   */
+  public FilteredSparseInstanceData(double[] attributeValues, int[] indexValues, int numberAttributes) {
+    super(attributeValues, indexValues, numberAttributes);
+  }
+
+
+  /**
+   * Value of the attribute in the indexAttribute position.
+   * If this value is absent, a NaN value (marker of missing value)
+   * is returned, otherwise this method returns the actual value.
+   *
+   * @param indexAttribute the index attribute
+   * @return the double
+   */
+  @Override
+  public double value(int indexAttribute) {
+    int location = locateIndex(indexAttribute);
+    if ((location >= 0) && (indexValues[location] == indexAttribute)) {
+      return attributeValues[location];
+    } else {
+      // returns a NaN value which represents missing values instead of a 0 (zero)
+      return Double.NaN;
+    }
+  }
+}
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/Instance.java b/samoa-instances/src/main/java/org/apache/samoa/instances/Instance.java
index da4dcdd..48a3a60 100644
--- a/samoa-instances/src/main/java/org/apache/samoa/instances/Instance.java
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/Instance.java
@@ -22,6 +22,9 @@
 
 import java.io.Serializable;
 
+/**
+ * The Interface Instance.
+ */
 public interface Instance extends Serializable {
 
   /**
@@ -47,6 +50,14 @@
   public Attribute attribute(int instAttIndex);
 
   /**
+   * Index of an Attribute.
+   *
+   * @param attribute, the attribute to be found.
+   * @return the index of an attribute
+   */
+  public int indexOfAttribute(Attribute attribute);
+
+  /**
    * Delete attribute at.
    *
    * @param i the index
@@ -70,8 +81,8 @@
   /**
    * Adds the sparse values.
    *
-   * @param indexValues the index values
-   * @param attributeValues the attribute values
+   * @param indexValues      the index values
+   * @param attributeValues  the attribute values
    * @param numberAttributes the number attributes
    */
   public void addSparseValues(int[] indexValues, double[] attributeValues, int numberAttributes);
@@ -100,20 +111,45 @@
   public double value(int instAttIndex);
 
   /**
+   * Gets the value of an attribute, given the attribute.
+   *
+   * @param attribute the attribute
+   * @return the double
+   */
+  public double value(Attribute attribute);
+
+  /**
    * Sets an attribute as missing
    *
-   * @param instAttIndex, the attribute's index     
+   * @param instAttIndex, the attribute's index
    */
-  public void setMissing(int instAttIndex);        
+  public void setMissing(int instAttIndex);
+
+
+  /**
+   * Sets an attribute as missing
+   *
+   * @param attribute, the Attribute
+   */
+  public void setMissing(Attribute attribute);
 
   /**
    * Sets the value of an attribute.
    *
    * @param instAttIndex the index
-   * @param value the value
+   * @param value        the value
    */
   public void setValue(int instAttIndex, double value);
 
+
+  /**
+   * Sets the value of an attribute.
+   *
+   * @param attribute, the Attribute
+   * @param value      the value
+   */
+  public void setValue(Attribute attribute, double value);
+
   /**
    * Checks if an attribute is missing.
    *
@@ -123,6 +159,14 @@
   public boolean isMissing(int instAttIndex);
 
   /**
+   * Checks if an attribute is missing.
+   *
+   * @param attribute, the Attribute
+   * @return true, if is missing
+   */
+  public boolean isMissing(Attribute attribute);
+
+  /**
    * Gets the index of the attribute given the index of the array in a sparse
    * representation.
    *
@@ -250,7 +294,7 @@
   /**
    * Sets the value of an output attribute.
    *
-   * @param indexClass the output attribute index
+   * @param indexClass     the output attribute index
    * @param valueAttribute the value of the attribute
    */
   public void setClassValue(int indexClass, double valueAttribute);
@@ -287,45 +331,4 @@
    */
   public double valueOutputAttribute(int attributeIndex);
 
-  /**
-   * Index of an Attribute.
-   *
-   * @param attribute, the attribute to be found.
-   * @return the index of an attribute
-   */
-  public int indexOfAttribute(Attribute attribute);
-
-  /**
-   * Gets the value of an attribute, given the attribute.
-   *
-   * @param attribute the attribute
-   * @return the double
-   */
-  public double value(Attribute attribute);
-
-  /**
-   * Sets an attribute as missing
-   *
-   * @param attribute, the Attribute
-   */
-  public void setMissing(Attribute attribute);
-
-  /**
-   * Sets the value of an attribute.
-   *
-   * @param attribute, the Attribute
-   * @param value the value
-   */
-  public void setValue(Attribute attribute, double value);
-
-  /**
-   * Checks if an attribute is missing.
-   *
-   * @param attribute, the Attribute
-   * @return true, if is missing
-   */
-  public boolean isMissing(Attribute attribute);
-
-
-
 }
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/InstanceData.java b/samoa-instances/src/main/java/org/apache/samoa/instances/InstanceData.java
index a5a5658..8eabdd2 100644
--- a/samoa-instances/src/main/java/org/apache/samoa/instances/InstanceData.java
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/InstanceData.java
@@ -22,6 +22,9 @@
 
 import java.io.Serializable;
 
+/**
+ * The Interface InstanceData.
+ */
 public interface InstanceData extends Serializable {
 
   /**
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/InstanceImpl.java b/samoa-instances/src/main/java/org/apache/samoa/instances/InstanceImpl.java
index e81c8a5..6a728cf 100644
--- a/samoa-instances/src/main/java/org/apache/samoa/instances/InstanceImpl.java
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/InstanceImpl.java
@@ -22,6 +22,9 @@
 
 import java.text.SimpleDateFormat;
 
+/**
+ * Implementation of Instance.
+ */
 public class InstanceImpl implements MultiLabelInstance {
 
   /**
@@ -52,6 +55,7 @@
   }
 
   //Dense
+
   /**
    * Instantiates a new instance.
    *
@@ -66,6 +70,7 @@
   }
 
   //Sparse
+
   /**
    * Instantiates a new instance.
    *
@@ -247,6 +252,19 @@
   }
 
   /**
+   * Value.
+   *
+   * @param attribute
+   *          the attribute
+   * @return the double
+   */
+  @Override
+  public double value(Attribute attribute) {
+    int index = this.instanceHeader.indexOf(attribute);
+    return value(index);
+  }
+
+  /**
    * String value.
    *
    * @param i
@@ -299,7 +317,6 @@
   @Override
   public int classIndex() {
     int classIndex = instanceHeader.classIndex();
-    //return classIndex != Integer.MAX_VALUE ? classIndex : 0;
     // return  ? classIndex : 0;
     if (classIndex == Integer.MAX_VALUE)
       if (this.instanceHeader.instanceInformation.range != null)
@@ -379,7 +396,11 @@
    */
   @Override
   public void setDataset(Instances dataset) {
-    this.instanceHeader = new InstancesHeader(dataset);
+    if (dataset instanceof InstancesHeader) {
+      this.instanceHeader = (InstancesHeader) dataset;
+    } else {
+      this.instanceHeader = new InstancesHeader(dataset);
+    }
   }
 
   /**
@@ -478,19 +499,6 @@
     this.setValue(instAttIndex, Double.NaN);
   }
 
-  /**
-   * Value.
-   *
-   * @param attribute
-   *          the attribute
-   * @return the double
-   */
-  @Override
-  public double value(Attribute attribute) {
-    int index = this.instanceHeader.indexOf(attribute);
-    return value(index);
-  }
-
   @Override
   public void setMissing(Attribute attribute) {
     int index = this.instanceHeader.indexOf(attribute);
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/InstanceInformation.java b/samoa-instances/src/main/java/org/apache/samoa/instances/InstanceInformation.java
index 9d39791..32d686e 100644
--- a/samoa-instances/src/main/java/org/apache/samoa/instances/InstanceInformation.java
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/InstanceInformation.java
@@ -23,6 +23,9 @@
 import java.io.Serializable;
 import java.util.List;
 
+/**
+ * The Class InstanceInformation.
+ */
 public class InstanceInformation implements Serializable {
 
   /**
@@ -42,14 +45,6 @@
    */
   protected Range range;
 
-  public Attribute inputAttribute(int w) {
-    return this.attributesInformation.attribute(inputAttributeIndex(w));
-  }
-
-  public Attribute outputAttribute(int w) {
-    return this.attributesInformation.attribute(outputAttributeIndex(w));
-  }
-
   /**
    * Instantiates a new instance information.
    *
@@ -60,6 +55,18 @@
     this.relationName = chunk.relationName;
     this.attributesInformation = chunk.attributesInformation;
     this.classIndex = chunk.classIndex;
+    this.range = chunk.range;
+  }
+
+  /**
+   * Instantiates a new instance information.
+   *
+   * @param st    the st
+   * @param input the input
+   */
+  public InstanceInformation(String st, Attribute[] input) {
+    this.relationName = st;
+    this.attributesInformation = new AttributesInformation(input, input.length);
   }
 
   /**
@@ -83,78 +90,62 @@
     this.attributesInformation = null;
   }
 
-  //Information Instances
-  /* (non-Javadoc)
-   * @see com.yahoo.labs.samoa.instances.InstanceInformationInterface#setRelationName(java.lang.String)
-   */
-  public void setRelationName(String string) {
-    this.relationName = string;
+  public Attribute inputAttribute(int w) {
+    return this.attributesInformation.attribute(inputAttributeIndex(w));
   }
 
-  /* (non-Javadoc)
-   * @see com.yahoo.labs.samoa.instances.InstanceInformationInterface#getRelationName()
-   */
+  public Attribute outputAttribute(int w) {
+    return this.attributesInformation.attribute(outputAttributeIndex(w));
+  }
+
+
   public String getRelationName() {
     return this.relationName;
   }
 
-  /* (non-Javadoc)
-   * @see com.yahoo.labs.samoa.instances.InstanceInformationInterface#classIndex()
-   */
+  public void setRelationName(String string) {
+    this.relationName = string;
+  }
+
   public int classIndex() {
     return this.classIndex;
   }
 
-  /* (non-Javadoc)
-   * @see com.yahoo.labs.samoa.instances.InstanceInformationInterface#setClassIndex(int)
-   */
   public void setClassIndex(int classIndex) {
     this.classIndex = classIndex;
   }
 
-  /* (non-Javadoc)
-   * @see com.yahoo.labs.samoa.instances.InstanceInformationInterface#classAttribute()
-   */
   public Attribute classAttribute() {
     return this.attribute(this.classIndex());
   }
 
-  /* (non-Javadoc)
-   * @see com.yahoo.labs.samoa.instances.InstanceInformationInterface#numAttributes()
-   */
   public int numAttributes() {
     return this.attributesInformation.numberAttributes;
   }
 
-  /* (non-Javadoc)
-   * @see com.yahoo.labs.samoa.instances.InstanceInformationInterface#attribute(int)
-   */
   public Attribute attribute(int w) {
     return this.attributesInformation.attribute(w);
   }
 
-  /* (non-Javadoc)
-   * @see com.yahoo.labs.samoa.instances.InstanceInformationInterface#numClasses()
-   */
   public int numClasses() {
     return this.attributesInformation.attribute(classIndex()).numValues();
   }
 
-  /* (non-Javadoc)
-   * @see com.yahoo.labs.samoa.instances.InstanceInformationInterface#deleteAttributeAt(java.lang.Integer)
-   */
-  public void deleteAttributeAt(Integer integer) {
+  public void deleteAttributeAt(int integer) {
     this.attributesInformation.deleteAttributeAt(integer);
+    if (this.classIndex > integer) {
+      this.classIndex--;
+    }
   }
 
-  /* (non-Javadoc)
-   * @see com.yahoo.labs.samoa.instances.InstanceInformationInterface#insertAttributeAt(com.yahoo.labs.samoa.instances.Attribute, int)
-   */
   public void insertAttributeAt(Attribute attribute, int i) {
     this.attributesInformation.insertAttributeAt(attribute, i);
+    if (this.classIndex >= i) {
+      this.classIndex++;
+    }
   }
 
-  public void setAttributes(List<Attribute> v) {
+  public void setAttributes(Attribute[] v) {
     if (this.attributesInformation == null)
       this.attributesInformation = new AttributesInformation();
     this.attributesInformation.setAttributes(v);
@@ -209,7 +200,7 @@
     this.range = range;
   }
 
-  public void setAttributes(List<Attribute> v, List<Integer> indexValues) {
+  public void setAttributes(Attribute[] v, int[] indexValues) {
     if (this.attributesInformation == null)
       this.attributesInformation = new AttributesInformation();
     this.attributesInformation.setAttributes(v, indexValues);
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/Instances.java b/samoa-instances/src/main/java/org/apache/samoa/instances/Instances.java
index 04fde39..1ee3876 100644
--- a/samoa-instances/src/main/java/org/apache/samoa/instances/Instances.java
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/Instances.java
@@ -30,6 +30,9 @@
 import java.util.List;
 import java.util.Random;
 
+/**
+ * Class Instances that stores a set of instances and their structure.
+ */
 public class Instances implements Serializable {
 
   /**
@@ -65,6 +68,16 @@
 
   transient protected Loader loader;
 
+/**
+   * Indices of relevant features.
+   */
+  protected int[] indicesRelevants;
+
+  /**
+   * Indices of irrelevant features.
+   */
+  protected int[] indicesIrrelevants;
+
   /**
    * Instantiates a new instances.
    *
@@ -73,6 +86,11 @@
   public Instances(Instances chunk) {
     this(chunk, chunk.numInstances());
     chunk.copyInstances(0, this, chunk.numInstances());
+    this.computeAttributesIndices();
+    if(chunk.indicesRelevants != null) {
+        this.indicesRelevants = chunk.indicesRelevants.clone();
+        this.indicesIrrelevants = chunk.indicesIrrelevants.clone();
+    }
   }
 
   /**
@@ -92,6 +110,7 @@
     this.loader = new ArffLoader(reader, 0, classAttribute);
     this.instanceInformation = loader.getStructure();
     this.instances = new ArrayList<Instance>();
+    this.computeAttributesIndices();
   }
 
   /**
@@ -101,9 +120,10 @@
    * @param range
    */
   public Instances(Reader reader, Range range) {
-    this.loader = new ArffLoader(reader, 0, classAttribute);//new MultiTargetArffLoader(reader, range);
+    this.loader = new MultiTargetArffLoader(reader, range); //new ArffLoader(reader, 0, classAttribute);
     this.instanceInformation = loader.getStructure();
     this.instances = new ArrayList<Instance>();
+    this.computeAttributesIndices();
   }
 
   public Instances(InputStream inputStream, int classAttribute, String encodingFormat) {
@@ -130,6 +150,24 @@
       capacity = 0;
     }
     this.instances = new ArrayList<Instance>(capacity);
+    this.computeAttributesIndices();
+    if(chunk.indicesRelevants != null) {
+        this.indicesRelevants = chunk.indicesRelevants.clone();
+        this.indicesIrrelevants = chunk.indicesIrrelevants.clone();
+    }
+  }
+
+    /**
+     * Instantiates a new instances.
+     *
+     * @param st the st
+     * @param v the v
+     * @param capacity the capacity
+     */
+    public Instances(String st, Attribute[] v, int capacity) {
+      this.instanceInformation = new InstanceInformation(st, v);
+      this.instances = new ArrayList<Instance>(capacity);
+      this.computeAttributesIndices();
   }
 
   /**
@@ -140,8 +178,13 @@
    * @param capacity the capacity
    */
   public Instances(String st, List<Attribute> v, int capacity) {
-    this.instanceInformation = new InstanceInformation(st, v);
+    Attribute[] attributes = new Attribute[v.size()];
+    for (int i = 0; i < v.size(); i++) {
+        attributes[i]= v.get(i);
+    }
+    this.instanceInformation = new InstanceInformation(st, attributes);
     this.instances = new ArrayList<Instance>(capacity);
+    this.computeAttributesIndices();
   }
 
   /**
@@ -160,6 +203,7 @@
           + "of range");
     }
     chunk.copyInstances(first, this, toCopy);
+    this.computeAttributesIndices();
   }
 
   /**
@@ -170,6 +214,7 @@
    */
   public Instances(StringReader st, int capacity) {
     this.instances = new ArrayList<Instance>(capacity);
+    this.computeAttributesIndices();
   }
 
   //Information Instances
@@ -253,21 +298,32 @@
    */
   public void deleteAttributeAt(Integer integer) {
     this.instanceInformation.deleteAttributeAt(integer);
+    for (int i = 0; i < numInstances(); i++) {
+      instance(i).setDataset(null);
+      instance(i).deleteAttributeAt(integer);
+      instance(i).setDataset(this);
+  }
   }
 
   /**
-   * Insert attribute at.
-   *
-   * @param attribute the attribute
-   * @param i the i
-   */
-  public void insertAttributeAt(Attribute attribute, int i) {
-    if (this.instanceInformation == null) {
-      this.instanceInformation = new InstanceInformation();
-    }
-    this.instanceInformation.insertAttributeAt(attribute, i);
+     * Insert attribute at.
+     *
+     * @param attribute the attribute
+     * @param position the position
+     */
+    public void insertAttributeAt(Attribute attribute, int position) {
+      if (this.instanceInformation == null) {
+          this.instanceInformation = new InstanceInformation();
+      }
+      this.instanceInformation.insertAttributeAt(attribute, position);
+      for (int i = 0; i < numInstances(); i++) {
+          instance(i).setDataset(null);
+          instance(i).insertAttributeAt(i);
+          instance(i).setDataset(this);
+      }
   }
 
+
   //List of Instances
   /**
    * Instance.
@@ -525,20 +581,31 @@
 
   }
 
-  public void setAttributes(List<Attribute> v) {
+ public void setAttributes(Attribute[] v) {
     if (this.instanceInformation == null) {
-      this.instanceInformation = new InstanceInformation();
+        this.instanceInformation = new InstanceInformation();
     }
     this.instanceInformation.setAttributes(v);
-  }
+}
 
-  public void setAttributes(List<Attribute> v, List<Integer> indexValues) {
+public void setAttributes(Attribute[] v, int[] indexValues) {
     if (this.instanceInformation == null) {
       this.instanceInformation = new InstanceInformation();
     }
     this.instanceInformation.setAttributes(v, indexValues);
   }
 
+  public void setAttributes(List<Attribute> v, List<Integer> indexValues) {
+    int[] ret = new int[indexValues.size()];
+    for(int i = 0;i < ret.length;i++)
+        ret[i] = indexValues.get(i);
+    Attribute[] attributes = new Attribute[v.size()];
+    for (int i = 0; i < v.size(); i++) {
+        attributes[i]= v.get(i);
+    }
+    setAttributes(attributes, ret);
+  }
+  
   /**
    * Returns the dataset as a string in ARFF format. Strings are quoted if
    * they contain whitespace characters, or if they are a question mark.
@@ -626,4 +693,48 @@
       hsAttributesIndices.put(this.attribute(i).name(), i);
     }
   }
+
+    /**
+     * Returns the indices of the relevant features indicesRelevants.
+     * @return indicesRelevants
+     */
+    public int[] getIndicesRelevants() {
+      return indicesRelevants;
+  }
+
+  /**
+   * Returns the indices of the irrelevant features indicesIrrelevants.
+   * @return indicesIrrelevants
+   */
+  public int[] getIndicesIrrelevants() {
+      return indicesIrrelevants;
+  }
+
+  /**
+   * Sets the indices of relevant features.
+   * This method also sets the irrelevant ones since
+   * it is the set complement.
+   *
+   * @param indicesRelevants
+   */
+  public void setIndicesRelevants(int[] indicesRelevants) {
+      this.indicesRelevants = indicesRelevants;
+      // -1 to skip the class attribute
+      int numIrrelevantFeatures = this.numAttributes() - this.indicesRelevants.length - 1;
+      this.indicesIrrelevants = new int[numIrrelevantFeatures];
+
+      // Infers and sets the set of irrelevant features
+      int index = 0;
+      int indexRel = 0;
+      for(int i = 0; i < numAttributes(); i++){
+          if(i != classIndex()) {
+              while (indexRel < indicesRelevants.length - 1 &&
+                      i > indicesRelevants[indexRel]) indexRel++;
+              if (indicesRelevants[indexRel] != i){
+                  indicesIrrelevants[index] = i;
+                  index++;
+              }
+          }
+      }
+  }
 }
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/InstancesHeader.java b/samoa-instances/src/main/java/org/apache/samoa/instances/InstancesHeader.java
index c32cf88..a58566f 100644
--- a/samoa-instances/src/main/java/org/apache/samoa/instances/InstancesHeader.java
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/InstancesHeader.java
@@ -20,6 +20,10 @@
  * #L%
  */
 
+ /**
+ * Class for storing the header or context of a data stream. It allows to know
+ * the number of attributes and classes.
+ */
 public class InstancesHeader extends Instances {
 
   private static final long serialVersionUID = 1L;
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/MultiLabelInstance.java b/samoa-instances/src/main/java/org/apache/samoa/instances/MultiLabelInstance.java
index 9567c90..9cfcb96 100644
--- a/samoa-instances/src/main/java/org/apache/samoa/instances/MultiLabelInstance.java
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/MultiLabelInstance.java
@@ -20,6 +20,9 @@
  * #L%
  */
 
+/**
+ * The Interface MultiLabelInstance.
+ */
 public interface MultiLabelInstance extends Instance {
 
 }
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/MultiLabelPrediction.java b/samoa-instances/src/main/java/org/apache/samoa/instances/MultiLabelPrediction.java
index 0b51c56..5b82294 100644
--- a/samoa-instances/src/main/java/org/apache/samoa/instances/MultiLabelPrediction.java
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/MultiLabelPrediction.java
@@ -21,47 +21,40 @@
  */
 
 import java.io.Serializable;
-import java.util.ArrayList;
 
 public class MultiLabelPrediction implements Prediction, Serializable {
-  protected ArrayList< ArrayList<Double> > prediction;
+  protected DoubleVector[] prediction;
 
   public MultiLabelPrediction() {
     this(0);
   }
 
   public MultiLabelPrediction(int numOutputAttributes) {
-    prediction = new ArrayList< ArrayList<Double> >();
-    for (int i=0; i<numOutputAttributes;i++)
-      prediction.add(new ArrayList<Double>());
+    prediction = new DoubleVector[numOutputAttributes];
+    for (int i = 0; i < numOutputAttributes; i++)
+      prediction[i] = new DoubleVector();
   }
 
   @Override
   public int numOutputAttributes() {
-    return prediction.size();
+    return prediction.length;
   }
 
   @Override
   public int numClasses(int outputAttributeIndex) {
     int ret = 0;
-    if (prediction.size() > outputAttributeIndex) {
-      ret =  prediction.get(outputAttributeIndex).size();
+    if (prediction.length > outputAttributeIndex) {
+      ret = prediction[outputAttributeIndex].numValues();
     }
     return ret;
   }
 
   @Override
   public double[] getVotes(int outputAttributeIndex) {
-    int s = prediction.get(outputAttributeIndex).size();
     double ret[] = null;
-    if (prediction.size() > outputAttributeIndex) {
-      ArrayList<Double> aux = prediction.get(outputAttributeIndex);
-      ret = new double[s];
-      for (int i =0;i < s;i++) {
-        ret[i] = aux.get(i).doubleValue();
-      }
+    if (prediction.length > outputAttributeIndex) {
+      ret = prediction[outputAttributeIndex].getArrayCopy();
     }
-
     return ret;
   }
 
@@ -71,54 +64,38 @@
   }
 
   @Override
+  public void setVotes(double[] votes) {
+    setVotes(0, votes);
+  }
+
+  @Override
   public double getVote(int outputAttributeIndex, int classIndex) {
     double ret = 0.0;
-    if (prediction.size() > outputAttributeIndex) {
-      ret = (classIndex >= 0 && classIndex < prediction.get(outputAttributeIndex).size()) ?
-          prediction.get(outputAttributeIndex).get(classIndex) : 0;
+    if (prediction.length > outputAttributeIndex) {
+      ret = prediction[outputAttributeIndex].getValue(classIndex);
     }
     return ret;
   }
 
   @Override
   public void setVotes(int outputAttributeIndex, double[] votes) {
-    for(int i=0; i<votes.length; i++) {
-      if (i >= prediction.get(outputAttributeIndex).size()) {
-        prediction.get(outputAttributeIndex).ensureCapacity(i+1);
-        while (prediction.get(outputAttributeIndex).size() < i+1) {
-          prediction.get(outputAttributeIndex).add(0.0);
-        }
-      }
-
-      prediction.get(outputAttributeIndex).set(i,votes[i]);
-    }
-  }
-
-  @Override
-  public void setVotes(double[] votes) {
-    setVotes(0, votes);
+    for (int i = 0; i < votes.length; i++)
+      prediction[outputAttributeIndex].setValue(i, votes[i]);
   }
 
   @Override
   public void setVote(int outputAttributeIndex, int classIndex, double vote) {
-    if (outputAttributeIndex >= prediction.get(outputAttributeIndex).size()) {
-      prediction.get(outputAttributeIndex).ensureCapacity(classIndex+1);
-      while (prediction.get(outputAttributeIndex).size() < classIndex+1) {
-        prediction.get(outputAttributeIndex).add(0.0);
-      }
-    }
+    prediction[outputAttributeIndex].setValue(classIndex, vote);
 
-    prediction.get(outputAttributeIndex).set(classIndex, vote);
   }
 
   @Override
-  public String toString(){
-    StringBuffer sb= new StringBuffer();
-    for (int i=0; i<prediction.size(); i++){
+  public String toString() {
+    StringBuffer sb = new StringBuffer();
+    for (int i = 0; i < prediction.length; i++) {
       sb.append("Out " + i + ": ");
-      for (int c=0; c<prediction.get(i).size(); c++)
-      {
-        sb.append(((int)(prediction.get(i).get(c)*1000)/1000.0)+ " ");
+      for (int c = 0; c < prediction[i].numValues(); c++) {
+        sb.append(((int) (prediction[i].getValue(c) * 1000) / 1000.0) + " ");
       }
     }
     return sb.toString();
@@ -126,14 +103,82 @@
 
   @Override
   public boolean hasVotesForAttribute(int outputAttributeIndex) {
-    if(prediction.size()<(outputAttributeIndex+1))
+    if (prediction.length < (outputAttributeIndex + 1))
       return false;
-    return (prediction.get(outputAttributeIndex).size()==0) ? false : true;
+    return (prediction[outputAttributeIndex].numValues() == 0) ? false : true;
   }
 
   @Override
   public int size() {
-    return prediction.size();
+    return prediction.length;
   }
 
-}
\ No newline at end of file
+  protected class DoubleVector implements Serializable {
+
+    private static final long serialVersionUID = 1L;
+
+    protected double[] array;
+
+    public DoubleVector() {
+      this.array = new double[0];
+    }
+
+    public DoubleVector(double[] toCopy) {
+      this.array = new double[toCopy.length];
+      System.arraycopy(toCopy, 0, this.array, 0, toCopy.length);
+    }
+
+    public int numValues() {
+      return this.array.length;
+    }
+
+    public void setValue(int i, double v) {
+      if (i >= this.array.length) {
+        setArrayLength(i + 1);
+      }
+      this.array[i] = v;
+    }
+
+    public void addToValue(int i, double v) {
+      if (i >= this.array.length) {
+        setArrayLength(i + 1);
+      }
+      this.array[i] += v;
+    }
+
+    // returns 0.0 for values outside of range
+    public double getValue(int i) {
+      return ((i >= 0) && (i < this.array.length)) ? this.array[i] : 0.0;
+    }
+
+
+    public int maxIndex() {
+      int max = -1;
+      for (int i = 0; i < this.array.length; i++) {
+        if ((max < 0) || (this.array[i] > this.array[max])) {
+          max = i;
+        }
+      }
+      return max;
+    }
+
+    public double[] getArrayCopy() {
+      double[] aCopy = new double[this.array.length];
+      System.arraycopy(this.array, 0, aCopy, 0, this.array.length);
+      return aCopy;
+    }
+
+    protected void setArrayLength(int l) {
+      double[] newArray = new double[l];
+      int numToCopy = this.array.length;
+      if (numToCopy > l) {
+        numToCopy = l;
+      }
+      System.arraycopy(this.array, 0, newArray, 0, numToCopy);
+      this.array = newArray;
+    }
+
+
+  }
+
+}
diff --git a/samoa-instances/src/main/java/org/apache/samoa/instances/SparseInstanceData.java b/samoa-instances/src/main/java/org/apache/samoa/instances/SparseInstanceData.java
index 940271a..338643d 100644
--- a/samoa-instances/src/main/java/org/apache/samoa/instances/SparseInstanceData.java
+++ b/samoa-instances/src/main/java/org/apache/samoa/instances/SparseInstanceData.java
@@ -23,6 +23,19 @@
 public class SparseInstanceData implements InstanceData {
 
   /**
+   * The attribute values.
+   */
+  protected double[] attributeValues;
+  /**
+   * The index values.
+   */
+  protected int[] indexValues;
+  /**
+   * The number of attributes.
+   */
+  protected int numberAttributes;
+
+  /**
    * Instantiates a new sparse instance data.
    *
    * @param attributeValues
@@ -50,11 +63,6 @@
   }
 
   /**
-   * The attribute values.
-   */
-  protected double[] attributeValues;
-
-  /**
    * Gets the attribute values.
    *
    * @return the attribute values
@@ -112,16 +120,6 @@
   }
 
   /**
-   * The index values.
-   */
-  protected int[] indexValues;
-
-  /**
-   * The number of attributes.
-   */
-  protected int numberAttributes;
-
-  /**
    * Gets the number of attributes.
    *
    * @return the int
@@ -313,7 +311,7 @@
   public void insertAttributeAt(int position) {
     if ((position < 0) || (position > numAttributes())) {
       throw new IllegalArgumentException("Can't insert attribute: index out "
-          + "of range");
+              + "of range");
     }
     int index = locateIndex(position);