splitDataOnUnivariateCriterion(
double[][] data)
{
int[] features = GetFeaturesForSplitCritertion();
//Store values for each col to help in parallelization
double[] minGini = new double[features.Length - 1];
double[] splitCriterion = new double[features.Length - 1];
int[] attrIdx = new int[features.Length - 1];
//for (int col = 0; col < data.Count()-1;col++)
//Assume last column is for value, d not compute gini split for target value
Parallel.For(0, features.Count() - 1, new ParallelOptions {
MaxDegreeOfParallelism = _maxParallelThreads
}, col =>
{
double gini;
minGini[col] = double.PositiveInfinity;
for (int row = 0; row < data[0].Count(); row++)
{
//gini = getGiniImpurity(col, data[col][row]);
gini = GetGiniImpurity(data, row, col);
//Compute Gini
if (gini < minGini[col])
{
attrIdx[col] = col;
splitCriterion[col] = data[col][row];
minGini[col] = gini;
}
if (minGini[col] == 0) //Perfect split point found, no need to continue further
{
break; //return ed;
}
} //If condition
}); //Main loop
//Find value with lowest minGini
int minIdx = 0;
for (int col = 1; col < minGini.Length; col++)
{
if (minGini[col] < minGini[minIdx])
{
minIdx = col;
}
}
SplittedAttributeData ed = new SplittedAttributeData()
{
AttributeIndex = attrIdx[minIdx],
SplittingCriteriaValue = splitCriterion[minIdx]
};
return(ed);
}
splitDataOnUnivariateCriterion(
double[][] data)
{
double entropyS;
double entropySv;
double entropySum;
double infoGain = 0;
double[] filteredTargetData;
Dictionary <double, long> freqs;
SplittedAttributeData ed = new SplittedAttributeData();
ed.SplittingCriteriaValue = double.NegativeInfinity;
entropyS = getEntropyOfTargetAttribute(data);
for (int idxCol = 0; idxCol < data.Count();
idxCol++)
{
entropySum = 0;
if (data[idxCol] != null &&
idxCol != _indexTargetAttribute) //Do not compute when data not present
{
freqs = InformationGain.Frequency(
data[idxCol]);
//key has value
foreach (double key in freqs.Keys)
{
if (key != _missingValue)
{
filteredTargetData =
getFilteredTargetValues(data, idxCol, key);
entropySv = InformationGain.EntropyShannon(filteredTargetData);
entropySum += ((double)filteredTargetData.Length /
(double)data[_indexTargetAttribute].Length)
* entropySv;
}
}
infoGain = entropyS - entropySum;
//Compute InfoGain
if (infoGain > ed.SplittingCriteriaValue)
{
ed.Freqs = freqs;
ed.AttributeIndex = idxCol;
ed.SplittingCriteriaValue = infoGain;
}
} //if condition
} //Main loop
return(ed);
}
//Make private member so that stack is not full
protected virtual DecisionTreeNode buildChildNodes(ConcurrentBag <long> trainingDataRowIndices,
double value,
DecisionTreeNode dtnParent)
{
DecisionTreeNode dtn = new DecisionTreeNode(dtnParent);
//Get all rows in Training Data
FilteredData fd = getFilteredDataForNode(dtn, value,
trainingDataRowIndices);
//Check if all target examples are same or not
//Their Entropy will be 0
if (fd.NumberOfRows <= _minimumNumberPerNode || isTargetDataSame(fd.FilteredDataValues)) //Attributes is empty
{
setAsTargetAttributeNode(fd.FilteredDataValues, dtn);
return(dtn);//No more children if attributeIndex is target Attributes
}
//Set data for current node
SplittedAttributeData ed =
splitDataOnUnivariateCriterion(fd.FilteredDataValues);
//Check for positive and negative examples
dtn.setAttributeValues(ed.AttributeIndex,
_attributeHeaders[ed.AttributeIndex]);
ConcurrentBag <long> newTrainingDataRowIndices =
fd.TrainingDataRowIndices;
fd = null; //Free Memory -> Clean up data, no longer needed
//Key has values
foreach (double key in ed.Freqs.Keys)
{
if (key != 999) //Dont add for missing values
{
dtn.addChild(key, buildChildNodes(newTrainingDataRowIndices,
key,
dtn)); //Key has value
}
}
return(dtn);
}
//Make private member so that stack is not full
protected DecisionTreeNode BuildChildNodes(ConcurrentBag <long> trainingDataRowIndices,
double value,
DecisionTreeNode dtnParent,
bool isLessThan)
{
DecisionTreeNode dtn = new DecisionTreeNode(dtnParent);
//Get all rows in Training Data
FilteredData fd = GetFilteredDataForNode(dtn, value,
trainingDataRowIndices,
isLessThan);
//Stopping Criterion
//Check if minimum number of nodes are there
//OR all target values are same
if (fd.NumberOfRows <= _minimumNumberPerNode ||
isTargetDataSame(fd.FilteredDataValues) || //Attributes is empty
(dtnParent != null && fd.TrainingDataRowIndices.Count == trainingDataRowIndices.Count) || //implies no split happened)
GetAdditionalStoppingCondition(dtn))
{
if (fd.NumberOfRows == 0) //Special case, use original data as node
{
fd = convertRowIndicesToFilteredData(trainingDataRowIndices);
}
setAsTargetAttributeNode(fd.FilteredDataValues, dtn);
return(dtn); //No more children if min attributes reached
}
//Set data for current node
SplittedAttributeData ed =
splitDataOnUnivariateCriterion(fd.FilteredDataValues);
//Check for positive and negative examples
dtn.setAttributeValues(ed.AttributeIndex,
_attributeHeaders[ed.AttributeIndex]);
//Store value in column ed.AttributeIndex based on which split was done
dtn.Value = ed.SplittingCriteriaValue;
ConcurrentBag <long> newTrainingDataRowIndices =
fd.TrainingDataRowIndices;
fd = null; //Free Memory -> Clean up data, no longer needed
//Key has values
//Add left node
if (ed.SplittingCriteriaValue != _missingValue) //Dont add for missing values
{
//0 if for left, 1 is for right.
//There wont be any conflict since each node will have only 2 children
//DecisionTreeNode dtnChild =
dtn.addChild(0, BuildChildNodes(newTrainingDataRowIndices,
ed.SplittingCriteriaValue,
dtn, true)); //Key has value
//dtnChild =
dtn.addChild(1, BuildChildNodes(newTrainingDataRowIndices,
ed.SplittingCriteriaValue,
dtn, false)); //Key has value
}
return(dtn);
}