Exemple #1
0
/*
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
}