// 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
}
/*
splitTreeByGain calculate the gain in all dataset, and split into two node:
left and right.
Return node with the split information.
*/
func (runtime *Runtime) splitTreeByGain(D tabula.ClasetInterface) (
node *binary.BTNode,
e error,
) {
node = &binary.BTNode{}
D.RecountMajorMinor()
// if dataset is empty return node labeled with majority classes in
// dataset.
nrow := D.GetNRow()
if nrow <= 0 {
if DEBUG >= 2 {
fmt.Printf("[cart] empty dataset (%s) : %v\n",
D.MajorityClass(), D)
}
node.Value = NodeValue{
IsLeaf: true,
Class: D.MajorityClass(),
Size: 0,
}
return node, nil
}
// if all dataset is in the same class, return node as leaf with class
// is set to that class.
single, name := D.IsInSingleClass()
if single {
if DEBUG >= 2 {
fmt.Printf("[cart] in single class (%s): %v\n", name,
D.GetColumns())
}
node.Value = NodeValue{
IsLeaf: true,
Class: name,
Size: nrow,
}
return node, nil
}
if DEBUG >= 2 {
fmt.Println("[cart] D:", D)
}
// calculate the Gini gain for each attribute.
gains := runtime.computeGain(D)
// get attribute with maximum Gini gain.
MaxGainIdx := gini.FindMaxGain(&gains)
MaxGain := gains[MaxGainIdx]
// if maxgain value is 0, use majority class as node and terminate
// the process
if MaxGain.GetMaxGainValue() == 0 {
if DEBUG >= 2 {
fmt.Println("[cart] max gain 0 with target",
D.GetClassAsStrings(),
" and majority class is ", D.MajorityClass())
}
node.Value = NodeValue{
IsLeaf: true,
Class: D.MajorityClass(),
Size: 0,
}
return node, nil
}
// using the sorted index in MaxGain, sort all field in dataset
tabula.SortColumnsByIndex(D, MaxGain.SortedIndex)
if DEBUG >= 2 {
fmt.Println("[cart] maxgain:", MaxGain)
}
// Now that we have attribute with max gain in MaxGainIdx, and their
// gain dan partition value in Gains[MaxGainIdx] and
// GetMaxPartValue(), we split the dataset based on type of max-gain
// attribute.
// If its continuous, split the attribute using numeric value.
// If its discrete, split the attribute using subset (partition) of
// nominal values.
var splitV interface{}
if MaxGain.IsContinu {
splitV = MaxGain.GetMaxPartGainValue()
} else {
attrPartV := MaxGain.GetMaxPartGainValue()
attrSubV := attrPartV.(tekstus.ListStrings)
splitV = attrSubV[0].Normalize()
}
if DEBUG >= 2 {
fmt.Println("[cart] maxgainindex:", MaxGainIdx)
fmt.Println("[cart] split v:", splitV)
}
node.Value = NodeValue{
SplitAttrName: D.GetColumn(MaxGainIdx).GetName(),
IsLeaf: false,
IsContinu: MaxGain.IsContinu,
Size: nrow,
SplitAttrIdx: MaxGainIdx,
SplitV: splitV,
}
dsL, dsR, e := tabula.SplitRowsByValue(D, MaxGainIdx, splitV)
if e != nil {
return node, e
}
splitL := dsL.(tabula.ClasetInterface)
splitR := dsR.(tabula.ClasetInterface)
// Set the flag to parent in attribute referenced by
// MaxGainIdx, so it will not computed again in the next round.
cols := splitL.GetColumns()
for x := range *cols {
if x == MaxGainIdx {
(*cols)[x].Flag = ColFlagParent
} else {
(*cols)[x].Flag = 0
}
}
cols = splitR.GetColumns()
for x := range *cols {
if x == MaxGainIdx {
(*cols)[x].Flag = ColFlagParent
} else {
(*cols)[x].Flag = 0
}
}
nodeLeft, e := runtime.splitTreeByGain(splitL)
if e != nil {
return node, e
}
nodeRight, e := runtime.splitTreeByGain(splitR)
if e != nil {
return node, e
}
node.SetLeft(nodeLeft)
node.SetRight(nodeRight)
return node, nil
}