One 、 explain

IG yes information gain Abbreviation , The Chinese name is information gain , It's a very effective way to select features ( Especially in the use of svm When classifying ). There is no detailed introduction here , Those who are interested can googling once .

chi-square Is a common feature selection method , In the article about seed word expansion , Detailed description , No more details here .

Two 、weka How to use in

1、 Feature filter code

package com.lvxinjian.alg.models.feature;
import java.nio.charset.Charset;
import java.util.ArrayList; import weka.attributeSelection.ASEvaluation;
import weka.attributeSelection.AttributeEvaluator;
import weka.attributeSelection.Ranker;
import weka.core.Instances; import com.iminer.tool.common.util.FileTool;
/**
* @Description : Use Weka The method of feature selection based on ( At present, we support IG、Chi-square)
*
*/
public class FeatureSelectorByWeka { /**
* @function Use weka Built in algorithms filter features
* @param eval Object instances of feature filtering methods
* @param data arff Formatted data
* @param maxNumberOfAttribute The maximum number of features supported
* @param outputPath lex The output file
* @throws Exception
*/
public void EvalueAndRank(ASEvaluation eval , Instances data ,int maxNumberOfAttribute , String outputPath) throws Exception
{
Ranker rank = new Ranker();
eval.buildEvaluator(data);
rank.search(eval, data); // Filter attributes according to a specific search algorithm Used here Ranker The algorithm is just an attribute according to InfoGain/Chi-square Sort the size of
int[] attrIndex = rank.search(eval, data); // Print result information Here we show the sorting result of the attributes
ArrayList<String> attributeWords = new ArrayList<String>();
for (int i = 0; i < attrIndex.length; i++) {
// If the weight is equal to 0, And then jump out of the loop
if (((AttributeEvaluator) eval).evaluateAttribute(attrIndex[i]) == 0)
break;
if (i >= maxNumberOfAttribute)
break;
attributeWords.add(i + "\t"
+ data.attribute(attrIndex[i]).name() + "\t" + "1");
}
FileTool.SaveListToFile(attributeWords, outputPath, false,
Charset.forName("utf8"));
} }
package com.lvxinjian.alg.models.feature;
import java.io.IOException;
import weka.attributeSelection.ASEvaluation;
import weka.attributeSelection.ChiSquaredAttributeEval;
import weka.attributeSelection.InfoGainAttributeEval;
import weka.core.Instances;
import weka.core.converters.ConverterUtils.DataSource; import com.iminer.alg.models.generatefile.ParameterUtils; /**
* @Description : IG、Chi-square Feature screening
*
*/
public class WekaFeatureSelector extends FeatureSelector{ /**
* The largest number of features
*/
private int maxFeatureNum = 10000;
/**
* Save path of feature file
*/
private String outputPath = null;
/**
* @Fields rule For feature filtering rules
*/
private String classname = "CLASS";
/**
* Feature selection methods , The default is IG
*/
private String selectMethod = "IG"; private boolean Initialization(String options){
try {
String [] paramArrayOfString = options.split(" "); // The maximum number of initialization features
String maxFeatureNum = ParameterUtils.getOption("maxFeatureNum", paramArrayOfString);
if(maxFeatureNum.length() != 0)
this.maxFeatureNum = Integer.parseInt(maxFeatureNum);
// Initialize category
String classname = ParameterUtils.getOption("class", paramArrayOfString);
if(classname.length() != 0)
this.classname = classname;
else{
System.out.println("use default class name(\"CLASS\")");
}
// Initialize feature save path
String outputPath = ParameterUtils.getOption("outputPath", paramArrayOfString);
if(outputPath.length() != 0)
this.outputPath = outputPath;
else{
System.out.println("please initialze output path.");
return false;
}
String selectMethod = ParameterUtils.getOption("selectMethod", paramArrayOfString);
if(selectMethod.length() != 0)
this.selectMethod = selectMethod;
else{
System.out.println("use default select method(IG)");
}
} catch (Exception e) {
e.printStackTrace();
return false;
}
return true;
}
@Override
public boolean selectFeature(Object obj ,String options) throws IOException {
try {
if(!Initialization(options))
return false;
Instances data = (Instances)obj;
data.setClass(data.attribute(this.classname));
ASEvaluation selector = null;
if(this.selectMethod.equals("IG"))
selector = new InfoGainAttributeEval();
else if(this.selectMethod.equals("CHI"))
selector = new ChiSquaredAttributeEval();
FeatureSelectorByWeka attributeSelector = new FeatureSelectorByWeka();
attributeSelector.EvalueAndRank(selector, data ,this.maxFeatureNum ,this.outputPath);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
} return true;
} public static void main(String [] args) throws Exception
{
String root = "C:\\Users\\Administrator\\Desktop\\12_05\\ model training \\1219\\";
WekaFeatureSelector selector = new WekaFeatureSelector();
Instances data = DataSource.read(root + "train.Bigram.arff");
String options = "-maxFeatureNum 10000 -outputPath lex.txt";
selector.selectFeature(data, options);
}
}

Reference resources :

weka Data mining ( Two )---- feature selection (IG、chi-square)

Weka Study four ( Attribute selection )

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