// SelectRandomFeature if NRandomFeature is greater than zero, select and
// compute gain in n random features instead of in all features
func (runtime *Runtime) SelectRandomFeature(D tabula.ClasetInterface) {
if runtime.NRandomFeature <= 0 {
// all features selected
return
}
ncols := D.GetNColumn()
// count all features minus class
nfeature := ncols - 1
if runtime.NRandomFeature >= nfeature {
// Do nothing if number of random feature equal or greater than
// number of feature in dataset.
return
}
// exclude class index and parent node index
excludeIdx := []int{D.GetClassIndex()}
cols := D.GetColumns()
for x, col := range *cols {
if (col.Flag & ColFlagParent) == ColFlagParent {
excludeIdx = append(excludeIdx, x)
} else {
(*cols)[x].Flag |= ColFlagSkip
}
}
// Select random features excluding feature in `excludeIdx`.
var pickedIdx []int
for x := 0; x < runtime.NRandomFeature; x++ {
idx := numerus.IntPickRandPositive(ncols, false, pickedIdx,
excludeIdx)
pickedIdx = append(pickedIdx, idx)
// Remove skip flag on selected column
col := D.GetColumn(idx)
col.Flag = col.Flag &^ ColFlagSkip
}
if DEBUG >= 1 {
fmt.Println("[cart] selected random features:", pickedIdx)
fmt.Println("[cart] selected columns :", D.GetColumns())
}
}
/*
computeGain calculate the gini index for each value in each attribute.
*/
func (runtime *Runtime) computeGain(D tabula.ClasetInterface) (
gains []gini.Gini,
) {
switch runtime.SplitMethod {
case SplitMethodGini:
// create gains value for all attribute minus target class.
gains = make([]gini.Gini, D.GetNColumn())
}
runtime.SelectRandomFeature(D)
classVS := D.GetClassValueSpace()
classIdx := D.GetClassIndex()
classType := D.GetClassType()
for x, col := range *D.GetColumns() {
// skip class attribute.
if x == classIdx {
continue
}
// skip column flagged with parent
if (col.Flag & ColFlagParent) == ColFlagParent {
gains[x].Skip = true
continue
}
// ignore column flagged with skip
if (col.Flag & ColFlagSkip) == ColFlagSkip {
gains[x].Skip = true
continue
}
// compute gain.
if col.GetType() == tabula.TReal {
attr := col.ToFloatSlice()
if classType == tabula.TString {
target := D.GetClassAsStrings()
gains[x].ComputeContinu(&attr, &target,
&classVS)
} else {
targetReal := D.GetClassAsReals()
classVSReal := tekstus.StringsToFloat64(
classVS)
gains[x].ComputeContinuFloat(&attr,
&targetReal, &classVSReal)
}
} else {
attr := col.ToStringSlice()
attrV := col.ValueSpace
if DEBUG >= 2 {
fmt.Println("[cart] attr :", attr)
fmt.Println("[cart] attrV:", attrV)
}
target := D.GetClassAsStrings()
gains[x].ComputeDiscrete(&attr, &attrV, &target,
&classVS)
}
if DEBUG >= 2 {
fmt.Println("[cart] gain :", gains[x])
}
}
return
}