def __init__(self, cond_samples=None):
        defaultdict.__init__(self, FreqDist)
        if cond_samples:
            for (cond, sample) in cond_samples:
                self[cond][sample] += 1
Construct a new empty conditional frequency distribution.  In
dataset/ETHPy150Open nltk/nltk/nltk/probability.py/ConditionalFreqDist.__init__