Class ConditionalFreqDist

source code

object --+
         |
        ConditionalFreqDist

A collection of frequency distributions for a single experiment run under different conditions. Conditional frequency distributions are used to record the number of times each sample occurred, given the condition under which the experiment was run. For example, a conditional frequency distribution could be used to record the frequency of each word (type) in a document, given its length. Formally, a conditional frequency distribution can be defined as a function that maps from each condition to the FreqDist for the experiment under that condition.

The frequency distribution for each condition is accessed using the indexing operator:

>>> cfdist[3]
<FreqDist with 73 outcomes>
>>> cfdist[3].freq('the')
0.4
>>> cfdist[3]['dog']
2

When the indexing operator is used to access the frequency distribution for a condition that has not been accessed before, ConditionalFreqDist creates a new empty FreqDist for that condition.

Conditional frequency distributions are typically constructed by repeatedly running an experiment under a variety of conditions, and incrementing the sample outcome counts for the appropriate conditions. For example, the following code will produce a conditional frequency distribution that encodes how often each word type occurs, given the length of that word type:

>>> cfdist = ConditionalFreqDist()
>>> for word in tokenize.whitespace(sent):
...     condition = len(word)
...     cfdist[condition].inc(word)

An equivalent way to do this is with the initializer:

>>> cfdist = ConditionalFreqDist((len(word), word) for word in tokenize.whitespace(sent))