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| <h2 title="Class FieldSelectionMapReduce" class="title">Class FieldSelectionMapReduce<K,V></h2> |
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| <li>org.apache.hadoop.mapred.lib.FieldSelectionMapReduce<K,V></li> |
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| <br> |
| <pre>@InterfaceAudience.Public |
| @InterfaceStability.Stable |
| public class <span class="typeNameLabel">FieldSelectionMapReduce<K,V></span> |
| extends <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</a> |
| implements <a href="../../../../../org/apache/hadoop/mapred/Mapper.html" title="interface in org.apache.hadoop.mapred">Mapper</a><K,V,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>>, <a href="../../../../../org/apache/hadoop/mapred/Reducer.html" title="interface in org.apache.hadoop.mapred">Reducer</a><<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>></pre> |
| <div class="block">This class implements a mapper/reducer class that can be used to perform |
| field selections in a manner similar to unix cut. The input data is treated |
| as fields separated by a user specified separator (the default value is |
| "\t"). The user can specify a list of fields that form the map output keys, |
| and a list of fields that form the map output values. If the inputformat is |
| TextInputFormat, the mapper will ignore the key to the map function. and the |
| fields are from the value only. Otherwise, the fields are the union of those |
| from the key and those from the value. |
| |
| The field separator is under attribute "mapreduce.fieldsel.data.field.separator" |
| |
| The map output field list spec is under attribute |
| "mapreduce.fieldsel.map.output.key.value.fields.spec". |
| The value is expected to be like "keyFieldsSpec:valueFieldsSpec" |
| key/valueFieldsSpec are comma (,) separated field spec: fieldSpec,fieldSpec,fieldSpec ... |
| Each field spec can be a simple number (e.g. 5) specifying a specific field, or a range |
| (like 2-5) to specify a range of fields, or an open range (like 3-) specifying all |
| the fields starting from field 3. The open range field spec applies value fields only. |
| They have no effect on the key fields. |
| |
| Here is an example: "4,3,0,1:6,5,1-3,7-". It specifies to use fields 4,3,0 and 1 for keys, |
| and use fields 6,5,1,2,3,7 and above for values. |
| |
| The reduce output field list spec is under attribute |
| "mapreduce.fieldsel.reduce.output.key.value.fields.spec". |
| |
| The reducer extracts output key/value pairs in a similar manner, except that |
| the key is never ignored.</div> |
| </li> |
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| <h3>Field Summary</h3> |
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| <th class="colLast" scope="col">Field and Description</th> |
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| <tr class="altColor"> |
| <td class="colFirst"><code>static org.slf4j.Logger</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html#LOG">LOG</a></span></code> </td> |
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| <tr> |
| <th class="colOne" scope="col">Constructor and Description</th> |
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| <td class="colOne"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html#FieldSelectionMapReduce--">FieldSelectionMapReduce</a></span>()</code> </td> |
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| <h3>Method Summary</h3> |
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| <caption><span id="t0" class="activeTableTab"><span>All Methods</span><span class="tabEnd"> </span></span><span id="t2" class="tableTab"><span><a href="javascript:show(2);">Instance Methods</a></span><span class="tabEnd"> </span></span><span id="t4" class="tableTab"><span><a href="javascript:show(8);">Concrete Methods</a></span><span class="tabEnd"> </span></span></caption> |
| <tr> |
| <th class="colFirst" scope="col">Modifier and Type</th> |
| <th class="colLast" scope="col">Method and Description</th> |
| </tr> |
| <tr id="i0" class="altColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html#close--">close</a></span>()</code> </td> |
| </tr> |
| <tr id="i1" class="rowColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html#configure-org.apache.hadoop.mapred.JobConf-">configure</a></span>(<a href="../../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred">JobConf</a> job)</code> |
| <div class="block">Initializes a new instance from a <a href="../../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred"><code>JobConf</code></a>.</div> |
| </td> |
| </tr> |
| <tr id="i2" class="altColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html#map-K-V-org.apache.hadoop.mapred.OutputCollector-org.apache.hadoop.mapred.Reporter-">map</a></span>(<a href="../../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html" title="type parameter in FieldSelectionMapReduce">K</a> key, |
| <a href="../../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html" title="type parameter in FieldSelectionMapReduce">V</a> val, |
| <a href="../../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</a><<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>> output, |
| <a href="../../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</a> reporter)</code> |
| <div class="block">The identify function.</div> |
| </td> |
| </tr> |
| <tr id="i3" class="rowColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html#reduce-org.apache.hadoop.io.Text-java.util.Iterator-org.apache.hadoop.mapred.OutputCollector-org.apache.hadoop.mapred.Reporter-">reduce</a></span>(<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a> key, |
| <a href="https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html?is-external=true" title="class or interface in java.util">Iterator</a><<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>> values, |
| <a href="../../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</a><<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>> output, |
| <a href="../../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</a> reporter)</code> |
| <div class="block"><i>Reduces</i> values for a given key.</div> |
| </td> |
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| <code><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#clone--" title="class or interface in java.lang">clone</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#equals-java.lang.Object-" title="class or interface in java.lang">equals</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#finalize--" title="class or interface in java.lang">finalize</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#getClass--" title="class or interface in java.lang">getClass</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#hashCode--" title="class or interface in java.lang">hashCode</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#notify--" title="class or interface in java.lang">notify</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#notifyAll--" title="class or interface in java.lang">notifyAll</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#toString--" title="class or interface in java.lang">toString</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#wait--" title="class or interface in java.lang">wait</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#wait-long-" title="class or interface in java.lang">wait</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#wait-long-int-" title="class or interface in java.lang">wait</a></code></li> |
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| <h4>LOG</h4> |
| <pre>public static final org.slf4j.Logger LOG</pre> |
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| <h4>FieldSelectionMapReduce</h4> |
| <pre>public FieldSelectionMapReduce()</pre> |
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| <a name="map-java.lang.Object-java.lang.Object-org.apache.hadoop.mapred.OutputCollector-org.apache.hadoop.mapred.Reporter-"> |
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| <h4>map</h4> |
| <pre>public void map(<a href="../../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html" title="type parameter in FieldSelectionMapReduce">K</a> key, |
| <a href="../../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html" title="type parameter in FieldSelectionMapReduce">V</a> val, |
| <a href="../../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</a><<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>> output, |
| <a href="../../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</a> reporter) |
| throws <a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></pre> |
| <div class="block">The identify function. Input key/value pair is written directly to output.</div> |
| <dl> |
| <dt><span class="overrideSpecifyLabel">Specified by:</span></dt> |
| <dd><code><a href="../../../../../org/apache/hadoop/mapred/Mapper.html#map-K1-V1-org.apache.hadoop.mapred.OutputCollector-org.apache.hadoop.mapred.Reporter-">map</a></code> in interface <code><a href="../../../../../org/apache/hadoop/mapred/Mapper.html" title="interface in org.apache.hadoop.mapred">Mapper</a><<a href="../../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html" title="type parameter in FieldSelectionMapReduce">K</a>,<a href="../../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html" title="type parameter in FieldSelectionMapReduce">V</a>,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>></code></dd> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>key</code> - the input key.</dd> |
| <dd><code>val</code> - the input value.</dd> |
| <dd><code>output</code> - collects mapped keys and values.</dd> |
| <dd><code>reporter</code> - facility to report progress.</dd> |
| <dt><span class="throwsLabel">Throws:</span></dt> |
| <dd><code><a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></code></dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="configure-org.apache.hadoop.mapred.JobConf-"> |
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| <h4>configure</h4> |
| <pre>public void configure(<a href="../../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred">JobConf</a> job)</pre> |
| <div class="block"><span class="descfrmTypeLabel">Description copied from interface: <code><a href="../../../../../org/apache/hadoop/mapred/JobConfigurable.html#configure-org.apache.hadoop.mapred.JobConf-">JobConfigurable</a></code></span></div> |
| <div class="block">Initializes a new instance from a <a href="../../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred"><code>JobConf</code></a>.</div> |
| <dl> |
| <dt><span class="overrideSpecifyLabel">Specified by:</span></dt> |
| <dd><code><a href="../../../../../org/apache/hadoop/mapred/JobConfigurable.html#configure-org.apache.hadoop.mapred.JobConf-">configure</a></code> in interface <code><a href="../../../../../org/apache/hadoop/mapred/JobConfigurable.html" title="interface in org.apache.hadoop.mapred">JobConfigurable</a></code></dd> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>job</code> - the configuration</dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="close--"> |
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| <h4>close</h4> |
| <pre>public void close() |
| throws <a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></pre> |
| <dl> |
| <dt><span class="overrideSpecifyLabel">Specified by:</span></dt> |
| <dd><code><a href="https://docs.oracle.com/javase/8/docs/api/java/io/Closeable.html?is-external=true#close--" title="class or interface in java.io">close</a></code> in interface <code><a href="https://docs.oracle.com/javase/8/docs/api/java/io/Closeable.html?is-external=true" title="class or interface in java.io">Closeable</a></code></dd> |
| <dt><span class="overrideSpecifyLabel">Specified by:</span></dt> |
| <dd><code><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/AutoCloseable.html?is-external=true#close--" title="class or interface in java.lang">close</a></code> in interface <code><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/AutoCloseable.html?is-external=true" title="class or interface in java.lang">AutoCloseable</a></code></dd> |
| <dt><span class="throwsLabel">Throws:</span></dt> |
| <dd><code><a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></code></dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="reduce-org.apache.hadoop.io.Text-java.util.Iterator-org.apache.hadoop.mapred.OutputCollector-org.apache.hadoop.mapred.Reporter-"> |
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| <h4>reduce</h4> |
| <pre>public void reduce(<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a> key, |
| <a href="https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html?is-external=true" title="class or interface in java.util">Iterator</a><<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>> values, |
| <a href="../../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</a><<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>> output, |
| <a href="../../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</a> reporter) |
| throws <a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></pre> |
| <div class="block"><span class="descfrmTypeLabel">Description copied from interface: <code><a href="../../../../../org/apache/hadoop/mapred/Reducer.html#reduce-K2-java.util.Iterator-org.apache.hadoop.mapred.OutputCollector-org.apache.hadoop.mapred.Reporter-">Reducer</a></code></span></div> |
| <div class="block"><i>Reduces</i> values for a given key. |
| |
| <p>The framework calls this method for each |
| <code><key, (list of values)></code> pair in the grouped inputs. |
| Output values must be of the same type as input values. Input keys must |
| not be altered. The framework will <b>reuse</b> the key and value objects |
| that are passed into the reduce, therefore the application should clone |
| the objects they want to keep a copy of. In many cases, all values are |
| combined into zero or one value. |
| </p> |
| |
| <p>Output pairs are collected with calls to |
| <a href="../../../../../org/apache/hadoop/mapred/OutputCollector.html#collect-K-V-"><code>OutputCollector.collect(Object,Object)</code></a>.</p> |
| |
| <p>Applications can use the <a href="../../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred"><code>Reporter</code></a> provided to report progress |
| or just indicate that they are alive. In scenarios where the application |
| takes a significant amount of time to process individual key/value |
| pairs, this is crucial since the framework might assume that the task has |
| timed-out and kill that task. The other way of avoiding this is to set |
| <a href="../../../../../../hadoop-mapreduce-client/hadoop-mapreduce-client-core/mapred-default.xml#mapreduce.task.timeout"> |
| mapreduce.task.timeout</a> to a high-enough value (or even zero for no |
| time-outs).</p></div> |
| <dl> |
| <dt><span class="overrideSpecifyLabel">Specified by:</span></dt> |
| <dd><code><a href="../../../../../org/apache/hadoop/mapred/Reducer.html#reduce-K2-java.util.Iterator-org.apache.hadoop.mapred.OutputCollector-org.apache.hadoop.mapred.Reporter-">reduce</a></code> in interface <code><a href="../../../../../org/apache/hadoop/mapred/Reducer.html" title="interface in org.apache.hadoop.mapred">Reducer</a><<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>,<a href="../../../../../org/apache/hadoop/io/Text.html" title="class in org.apache.hadoop.io">Text</a>></code></dd> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>key</code> - the key.</dd> |
| <dd><code>values</code> - the list of values to reduce.</dd> |
| <dd><code>output</code> - to collect keys and combined values.</dd> |
| <dd><code>reporter</code> - facility to report progress.</dd> |
| <dt><span class="throwsLabel">Throws:</span></dt> |
| <dd><code><a href="https://docs.oracle.com/javase/8/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</a></code></dd> |
| </dl> |
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