// ============================= classification =============================
protected StringTrainSpace mergeTrainSpaces(List<StringTrainSpace> spaces, int labelCutoff, int featureCutoff)
{
StringTrainSpace space;
if (spaces.size() == 1)
{
space = spaces.get(0);
}
else
{
System.out.println("Merging training instances:");
space = new StringTrainSpace(false, labelCutoff, featureCutoff);
for (StringTrainSpace s : spaces)
{
space.appendSpace(s);
System.out.print(".");
s.clear();
}
System.out.println();