/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
*/
package org.apache.hadoop.mapreduce.lib.fieldsel;
import java.util.List;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.io.Text;
/**
* 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.
*
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public class FieldSelectionHelper {
public static Text emptyText = new Text("");
public static final String DATA_FIELD_SEPERATOR =
"mapreduce.fieldsel.data.field.separator";
public static final String MAP_OUTPUT_KEY_VALUE_SPEC =
"mapreduce.fieldsel.map.output.key.value.fields.spec";
public static final String REDUCE_OUTPUT_KEY_VALUE_SPEC =
"mapreduce.fieldsel.reduce.output.key.value.fields.spec";
/**
* Extract the actual field numbers from the given field specs.
* If a field spec is in the form of "n-" (like 3-), then n will be the
* return value. Otherwise, -1 will be returned.
* @param fieldListSpec an array of field specs
* @param fieldList an array of field numbers extracted from the specs.
* @return number n if some field spec is in the form of "n-", -1 otherwise.
*/
private static int extractFields(String[] fieldListSpec,
List<Integer> fieldList) {
int allFieldsFrom = -1;
int i = 0;
int j = 0;
int pos = -1;
String fieldSpec = null;
for (i = 0; i < fieldListSpec.length; i++) {
fieldSpec = fieldListSpec[i];
if (fieldSpec.length() == 0) {
continue;
}
pos = fieldSpec.indexOf('-');
if (pos < 0) {
Integer fn = new Integer(fieldSpec);
fieldList.add(fn);
} else {
String start = fieldSpec.substring(0, pos);
String end = fieldSpec.substring(pos + 1);
if (start.length() == 0) {
start = "0";
}
if (end.length() == 0) {
allFieldsFrom = Integer.parseInt(start);
continue;
}
int startPos = Integer.parseInt(start);
int endPos = Integer.parseInt(end);
for (j = startPos; j <= endPos; j++) {
fieldList.add(j);
}
}
}
return allFieldsFrom;
}
private static String selectFields(String[] fields, List<Integer> fieldList,
int allFieldsFrom, String separator) {
String retv = null;
int i = 0;
StringBuffer sb = null;
if (fieldList != null && fieldList.size() > 0) {
if (sb == null) {
sb = new StringBuffer();
}
for (Integer index : fieldList) {
if (index < fields.length) {
sb.append(fields[index]);
}
sb.append(separator);
}
}
if (allFieldsFrom >= 0) {
if (sb == null) {
sb = new StringBuffer();
}
for (i = allFieldsFrom; i < fields.length; i++) {
sb.append(fields[i]).append(separator);
}
}
if (sb != null) {
retv = sb.toString();
if (retv.length() > 0) {
retv = retv.substring(0, retv.length() - 1);
}
}
return retv;
}
public static int parseOutputKeyValueSpec(String keyValueSpec,
List<Integer> keyFieldList, List<Integer> valueFieldList) {
String[] keyValSpecs = keyValueSpec.split(":", -1);
String[] keySpec = keyValSpecs[0].split(",");
String[] valSpec = new String[0];
if (keyValSpecs.length > 1) {
valSpec = keyValSpecs[1].split(",");
}
FieldSelectionHelper.extractFields(keySpec, keyFieldList);
return FieldSelectionHelper.extractFields(valSpec, valueFieldList);
}
public static String specToString(String fieldSeparator, String keyValueSpec,
int allValueFieldsFrom, List<Integer> keyFieldList,
List<Integer> valueFieldList) {
StringBuffer sb = new StringBuffer();
sb.append("fieldSeparator: ").append(fieldSeparator).append("\n");
sb.append("keyValueSpec: ").append(keyValueSpec).append("\n");
sb.append("allValueFieldsFrom: ").append(allValueFieldsFrom);
sb.append("\n");
sb.append("keyFieldList.length: ").append(keyFieldList.size());
sb.append("\n");
for (Integer field : keyFieldList) {
sb.append("\t").append(field).append("\n");
}
sb.append("valueFieldList.length: ").append(valueFieldList.size());
sb.append("\n");
for (Integer field : valueFieldList) {
sb.append("\t").append(field).append("\n");
}
return sb.toString();
}
private Text key = null;
private Text value = null;
public FieldSelectionHelper() {
}
public FieldSelectionHelper(Text key, Text val) {
this.key = key;
this.value = val;
}
public Text getKey() {
return key;
}
public Text getValue() {
return value;
}
public void extractOutputKeyValue(String key, String val,
String fieldSep, List<Integer> keyFieldList, List<Integer> valFieldList,
int allValueFieldsFrom, boolean ignoreKey, boolean isMap) {
if (!ignoreKey) {
val = key + val;
}
String[] fields = val.split(fieldSep);
String newKey = selectFields(fields, keyFieldList, -1, fieldSep);
String newVal = selectFields(fields, valFieldList, allValueFieldsFrom,
fieldSep);
if (isMap && newKey == null) {
newKey = newVal;
newVal = null;
}
if (newKey != null) {
this.key = new Text(newKey);
}
if (newVal != null) {
this.value = new Text(newVal);
}
}
}