[Numpy-discussion] Fast histogram

Jae-Joon Lee lee.j.joon@gmail....
Thu Apr 17 12:12:36 CDT 2008


>  But even if indices = array, one still needs to do something like:
>  for index in indices: histogram[index] += 1
>
>  Which is slow in python and fast in C.
>
>  I'm guessing that there's no utility function in numpy that does a
>  loop like this? If so, that would be handy, but if now, I think I need
>  to dig out the numpy book and write a little extension...
>

numpy.bincount?

Docstring:
    bincount(x,weights=None)

    Return the number of occurrences of each value in x.

    x must be a list of non-negative integers.  The output, b[i],
    represents the number of times that i is found in x.  If weights
    is specified, every occurrence of i at a position p contributes
    weights[p] instead of 1.

    See also: histogram, digitize, unique.

-JJ


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