How to do weighted random sample of categories in python

Question

Given a list of tuples where each tuple consists of a probability and an item I\'d like to sample an item according to its probability. For example, give the list [ (.3, \'a\'),

Answer 1

I reckon the multinomial function is a still fairly easy way to get samples of a distribution in random order. This is just one way

import numpy
from itertools import izip

def getSamples(input, size):
    probabilities, items = zip(*input)
    sampleCounts = numpy.random.multinomial(size, probabilities)
    samples = numpy.array(tuple(countsToSamples(sampleCounts, items)))
    numpy.random.shuffle(samples)
    return samples

def countsToSamples(counts, items):
    for value, repeats in izip(items, counts):
        for _i in xrange(repeats):
            yield value

Where inputs is as specified [(.2, 'a'), (.4, 'b'), (.3, 'c')] and size is the number of samples you need.