WEKA：由程式產生資料庫 Instances

WEKA API 請參閱官方網站：http://www.cs.waikato.ac.nz/ml/weka/

由於 WEKA 有自己專用的檔案格式 ARFF
但資料在記憶體中做完 preprocessing 以後，還得特地存成 *.arff 檔
再叫 WEKA 的 API 把 *.arff 檔讀進來，顯然是很蠢的事情=..=~
經過一番尋找，總算在官方文件中發現產生 Instances 資料庫的方法了！

可參閱：Creating an ARFF file

範例程式碼

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FastVector      atts; FastVector      attsRel; FastVector      attVals; FastVector      attValsRel; Instances       data; Instances       dataRel; double[]        vals; double[]        valsRel; int             i;   // 1. set up attributes atts = new FastVector(); // - numeric atts.addElement(new Attribute("att1")); // - nominal attVals = new FastVector(); for (i = 0; i < 5; i++)   attVals.addElement("val" + (i+1)); atts.addElement(new Attribute("att2", attVals)); // - string atts.addElement(new Attribute("att3", (FastVector) null)); // - date atts.addElement(new Attribute("att4", "yyyy-MM-dd")); // - relational attsRel = new FastVector(); // -- numeric attsRel.addElement(new Attribute("att5.1")); // -- nominal attValsRel = new FastVector(); for (i = 0; i < 5; i++)   attValsRel.addElement("val5." + (i+1)); attsRel.addElement(new Attribute("att5.2", attValsRel)); dataRel = new Instances("att5", attsRel, 0); atts.addElement(new Attribute("att5", dataRel, 0));      // 2. create Instances object data = new Instances("MyRelation", atts, 0);      // 3. fill with data // first instance vals = new double[data.numAttributes()]; // - numeric vals[0] = Math.PI; // - nominal vals[1] = attVals.indexOf("val3"); // - string vals[2] = data.attribute(2).addStringValue("This is a string!"); // - date vals[3] = data.attribute(3).parseDate("2001-11-09"); // - relational dataRel = new Instances(data.attribute(4).relation(), 0); // add data.add(new Instance(1.0, vals));      // second instance vals = new double[data.numAttributes()];  // important: needs NEW array! // - numeric vals[0] = Math.E; // - nominal vals[1] = attVals.indexOf("val1"); // - string vals[2] = data.attribute(2).addStringValue("And another one!"); // - date vals[3] = data.attribute(3).parseDate("2000-12-01"); // - relational dataRel = new Instances(data.attribute(4).relation(), 0); // -- first instance valsRel = new double[2]; valsRel[0] = Math.E + 1; valsRel[1] = attValsRel.indexOf("val5.4"); dataRel.add(new Instance(1.0, valsRel)); // -- second instance valsRel = new double[2]; valsRel[0] = Math.E + 2; valsRel[1] = attValsRel.indexOf("val5.1"); dataRel.add(new Instance(1.0, valsRel)); vals[4] = data.attribute(4).addRelation(dataRel); // add data.add(new Instance(1.0, vals));   //4. output data System.out.println(data);

輸出的結果如下：

@relation MyRelation

@attribute att1 numeric
@attribute att2 {val1,val2,val3,val4,val5}
@attribute att3 string
@attribute att4 date yyyy-MM-dd
@attribute att5 relational
@attribute att5.1 numeric
@attribute att5.2 {val5.1,val5.2,val5.3,val5.4,val5.5}
@end att5

@data
3.141593,val3,'This is a string!',2001-11-09,'3.718282,val5.4\n4.718282,val5.1'
2.718282,val1,'And another one!',2000-12-01,'3.718282,val5.4\n4.718282,val5.1'