Python - Count occurrences of certain ranges in a list

Question

So basically I want to count the number of occurrences a floating point appears in a given list. For example: a list of grades (all scores out of 100) are inputted by the user and they are sorted in groups of ten. How many times do scores from 0-10, 10-20, 20-30.. etc) appear? Like test score distribution. I know I can use the count function but since I'm not looking for specific numbers I'm having trouble. Is there a away to combine the count and range? Thanks for any help.

Answer 1

To group the data, divide it by the interval width. To count the number in each group, consider using collections.Counter. Here's a worked out example with documentation and a test:

from collections import Counter

def histogram(iterable, low, high, bins):
    '''Count elements from the iterable into evenly spaced bins

        >>> scores = [82, 85, 90, 91, 70, 87, 45]
        >>> histogram(scores, 0, 100, 10)
        [0, 0, 0, 0, 1, 0, 0, 1, 3, 2]

    '''
    step = (high - low + 0.0) / bins
    dist = Counter((float(x) - low) // step for x in iterable)
    return [dist[b] for b in range(bins)]

if __name__ == '__main__':
    import doctest
    print doctest.testmod()

Answer 2

If you are fine with using the external library NumPy, then you just need to call numpy.histogram():

>>> data = [82, 85, 90, 91, 70, 87, 45]
>>> counts, bins = numpy.histogram(data, bins=10, range=(0, 100))
>>> counts
array([0, 0, 0, 0, 1, 0, 0, 1, 3, 2])
>>> bins
array([   0.,   10.,   20.,   30.,   40.,   50.,   60.,   70.,   80.,
         90.,  100.])