//----------------------------------------------------------------------------
NodePtr create(const SampleVector& samples, unsigned int num_tests)
{
auto hist_samples = std::make_unique<HistogramType>(samples);
std::vector<SampleType> samples_left;
std::vector<SampleType> samples_right;
float max_info_gain = -0.1f;
NodePtr max_node;
for (unsigned int i = 0; i < num_tests; ++i)
{
NodePtr node(createRandomNode(m_log_stream));
samples_left.clear();
samples_right.clear();
//node->setThreshold(samples);
node->split(samples, samples_left, samples_right);
HistogramType hist_left(samples_left);
HistogramType hist_right(samples_right);
std::vector<HistogramType*> hist;
hist.push_back(&hist_left);
hist.push_back(&hist_right);
float infoGain = hist_samples->informationGain(hist);
*m_log_stream << ": IGain: " << infoGain << " / " << max_info_gain << ";" << i << ": " << samples_left.size() << "," << samples_right.size() << std::endl;
if (infoGain > max_info_gain)
{
max_info_gain = infoGain;
max_node = std::move(node);
}
}
max_node->setHistogram(std::move(hist_samples));
return max_node;
}
void Tree::trainTree(const MatrixReal& featMat, const VectorInteger& labels)
{
// We work with a queue of nodes, initially containing only the root node.
// We process the queue until it becomes empty.
std::queue<int> toTrain;
int size,numClasses,numVars,dims;
size = labels.size();
dims = featMat.cols();
numClasses = labels.maxCoeff();
classWts = VectorReal::Zero(numClasses+1);
for(int i = 0; i < labels.size(); ++i)
classWts(labels(i)) += 1.0;
classWts /= size;
for(int i = 0; i < size; ++i)
nodeix.push_back(i);
std::cout<<"Training tree, dimensions set\n";
numVars = (int)((double)sqrt((double)dims)) + 1;
int cur;
// The relevant indices for the root node is the entire set of training data
nodes[0].start = 0;
nodes[0].end = size-1;
// Initialise the queue with just the root node
toTrain.push(0);
// Stores the relevant features.
VectorReal relFeat;
// Resize our boolean array, more on this later.
indices.resize(size);
std::cout<<"Starting the queue\n";
int lpoints,rpoints;
// While the queue isn't empty, continue processing.
while(!toTrain.empty())
{
int featNum;
double threshold;
lpoints = rpoints = 0;
cur = toTrain.front();
// std::cout<<"In queue, node being processed is d :"<<cur.depth<<"\n";
// There are two ways for a node to get out of the queue trivially,
// a) it doesn't have enough data to be a non-trivial split, or
// b) it has hit the maximum permissible depth
if((nodes[cur].end - nodes[cur].start < DATA_MIN) || (nodes[cur].depth == depth))
{
// Tell ourselves that this is a leaf node, and remove the node
// from the queue.
// std::cout<<"Popping a leaf node\n";
nodes[cur].setType(true);
// Initialize the histogram and set it to zero
nodes[cur].hist = VectorReal::Zero(numClasses+1);
// The below code should give the histogram of all the elements
for(int i = nodes[cur].start; i <= nodes[cur].end; ++i)
{
nodes[cur].hist[labels(nodeix[i])] += 1.0;
}
for(int i = 0 ; i < classWts.size(); ++i)
nodes[cur].hist[i] = nodes[cur].hist[i] / classWts[i];
toTrain.pop();
continue;
}
double infoGain(-100.0);
relFeat.resize(size);
// In case this isn't a trivial node, we need to process it.
for(int i = 0; i < numVars; ++i)
{
// std::cout<<"Choosing a random variable\n";
// Randomly select a feature
featNum = rand()%dims;
// std::cout<<"Feat: "<<featNum<<std::endl;
// Extract the relevant feature set from the training data
relFeat = featMat.col(featNum);
double tmax,tmin,curInfo;
tmax = relFeat.maxCoeff();
tmin = relFeat.minCoeff();
// infoGain = -100;
//std::cout<<"Min "<<tmin<<"Max: "<<tmax<<std::endl;
// NUM_CHECKS is a macro defined at the start
for(int j = 0; j < NUM_CHECKS; ++j)
{
// std::cout<<"Choosing a random threshold\n";
// Generate a random threshold
threshold = ((rand()%100)/100.0)*(tmax - tmin) + tmin;
//std::cout<<"Thresh: "<<threshold<<std::endl;
for(int k = nodes[cur].start; k <= nodes[cur].end ; ++k)
indices[k] = (relFeat(k) < threshold);
// Check if we have enough information gain
curInfo = informationGain(nodes[cur].start,nodes[cur].end, labels);
// std::cout<<"Info gain : "<<curInfo<<"\n";
// curInfo = (double) ((rand()%10)/10.0);
if(curInfo > infoGain)
{
infoGain = curInfo;
nodes[cur].x = featNum;
nodes[cur].threshold = threshold;
}
}
}
// We have selected a feature and a threshold for it that maximises the information gain.
relFeat = featMat.col(nodes[cur].x);
// We just set the indices depending on whether the features are greater or lesser.
// Conventions followed : greater goes to the right.
for(int k = nodes[cur].start; k <= nodes[cur].end; ++k)
{
// If relfeat is lesser, indices[k] will be true, which will put it in the
// left side of the partition.
indices[k] = relFeat(k) < nodes[cur].threshold;
// indices[k] = (bool)(rand()%2);
if(indices[k])
lpoints++;
else
rpoints++;
}
if( (lpoints < DATA_MIN) || (rpoints < DATA_MIN) )
{
// Tell ourselves that this is a leaf node, and remove the node
// from the queue.
// std::cout<<"Popping a leaf node\n";
nodes[cur].setType(true);
// Initialize the histogram and set it to zero
nodes[cur].hist.resize(numClasses+1);
nodes[cur].hist = VectorReal::Zero(numClasses+1);
// The below code should give the histogram of all the elements
for(int i = nodes[cur].start; i <= nodes[cur].end; ++i)
{
nodes[cur].hist[labels(nodeix[i])] += 1.0;
}
toTrain.pop();
continue;
}
int part;
// Use the prebuilt function to linearly partition our data
part = partition(nodes[cur].start,nodes[cur].end);
Node right, left;
// Increase the depth of the children
right.depth = left.depth = nodes[cur].depth + 1;
// Correctly assign the partitions
left.start = nodes[cur].start;
left.end = part -1;
// Push back into the relevant places and also link the parent and the child
nodes.push_back(left);
nodes[cur].leftChild = nodes.size()-1;
toTrain.push(nodes[cur].leftChild);
// Ditto with the right node.
right.start = part;
right.end = nodes[cur].end;
nodes.push_back(right);
nodes[cur].rightChild = nodes.size()-1;
toTrain.push(nodes[cur].rightChild);
// Finally remove our node from the queue.
toTrain.pop();
}
}