MLlib is Spark's scalable machine learning library consisting of common learning algorithms and utilities, including classification, regression, clustering, collaborative filtering, dimensionality reduction, as well as underlying optimization primitives, as outlined below:
MLlib is under active development. The APIs marked Experimental
/DeveloperApi
may change in future releases, and the migration guide below will explain all changes between releases.
MLlib uses the linear algebra package Breeze, which depends on netlib-java, and jblas. netlib-java
and jblas
depend on native Fortran routines. You need to install the gfortran runtime library if it is not already present on your nodes. MLlib will throw a linking error if it cannot detect these libraries automatically. Due to license issues, we do not include netlib-java
‘s native libraries in MLlib’s dependency set under default settings. If no native library is available at runtime, you will see a warning message. To use native libraries from netlib-java
, please build Spark with -Pnetlib-lgpl
or include com.github.fommil.netlib:all:1.1.2
as a dependency of your project. If you want to use optimized BLAS/LAPACK libraries such as OpenBLAS, please link its shared libraries to /usr/lib/libblas.so.3
and /usr/lib/liblapack.so.3
, respectively. BLAS/LAPACK libraries on worker nodes should be built without multithreading.
To use MLlib in Python, you will need NumPy version 1.4 or newer.
The only API changes in MLlib v1.1 are in DecisionTree
, which continues to be an experimental API in MLlib 1.1:
(Breaking change) The meaning of tree depth has been changed by 1 in order to match the implementations of trees in scikit-learn and in rpart. In MLlib v1.0, a depth-1 tree had 1 leaf node, and a depth-2 tree had 1 root node and 2 leaf nodes. In MLlib v1.1, a depth-0 tree has 1 leaf node, and a depth-1 tree has 1 root node and 2 leaf nodes. This depth is specified by the maxDepth
parameter in Strategy
or via DecisionTree
static trainClassifier
and trainRegressor
methods.
(Non-breaking change) We recommend using the newly added trainClassifier
and trainRegressor
methods to build a DecisionTree
, rather than using the old parameter class Strategy
. These new training methods explicitly separate classification and regression, and they replace specialized parameter types with simple String
types.
Examples of the new, recommended trainClassifier
and trainRegressor
are given in the Decision Trees Guide.
In MLlib v1.0, we support both dense and sparse input in a unified way, which introduces a few breaking changes. If your data is sparse, please store it in a sparse format instead of dense to take advantage of sparsity in both storage and computation. Details are described below.
We used to represent a feature vector by Array[Double]
, which is replaced by Vector
in v1.0. Algorithms that used to accept RDD[Array[Double]]
now take RDD[Vector]
. LabeledPoint
is now a wrapper of (Double, Vector)
instead of (Double, Array[Double])
. Converting Array[Double]
to Vector
is straightforward:
{% highlight scala %} import org.apache.spark.mllib.linalg.{Vector, Vectors}
val array: Array[Double] = ... // a double array val vector: Vector = Vectors.dense(array) // a dense vector {% endhighlight %}
Vectors
provides factory methods to create sparse vectors.
Note: Scala imports scala.collection.immutable.Vector
by default, so you have to import org.apache.spark.mllib.linalg.Vector
explicitly to use MLlib's Vector
.
We used to represent a feature vector by double[]
, which is replaced by Vector
in v1.0. Algorithms that used to accept RDD<double[]>
now take RDD<Vector>
. LabeledPoint
is now a wrapper of (double, Vector)
instead of (double, double[])
. Converting double[]
to Vector
is straightforward:
{% highlight java %} import org.apache.spark.mllib.linalg.Vector; import org.apache.spark.mllib.linalg.Vectors;
double[] array = ... // a double array Vector vector = Vectors.dense(array); // a dense vector {% endhighlight %}
Vectors
provides factory methods to create sparse vectors.
We used to represent a labeled feature vector in a NumPy array, where the first entry corresponds to the label and the rest are features. This representation is replaced by class LabeledPoint
, which takes both dense and sparse feature vectors.
{% highlight python %} from pyspark.mllib.linalg import SparseVector from pyspark.mllib.regression import LabeledPoint
pos = LabeledPoint(1.0, [1.0, 0.0, 3.0])
neg = LabeledPoint(0.0, SparseVector(3, [0, 2], [1.0, 3.0])) {% endhighlight %}