Is there a MATLAB accumarray equivalent in numpy?

Question

I\'m looking for a fast solution to MATLAB\'s accumarray in numpy. The accumarray accumulates the elements of an array which belong to the same index. An exampl

Answer 1

How about the following:

import numpy

def accumarray(a, accmap):

    ordered_indices = numpy.argsort(accmap)

    ordered_accmap = accmap[ordered_indices]

    _, sum_indices = numpy.unique(ordered_accmap, return_index=True)

    cumulative_sum = numpy.cumsum(a[ordered_indices])[sum_indices-1]

    result = numpy.empty(len(sum_indices), dtype=a.dtype)
    result[:-1] = cumulative_sum[1:]
    result[-1] = cumulative_sum[0]

    result[1:] = result[1:] - cumulative_sum[1:]

    return result