Does NumPy have an inverse of unravel_index()?

Question

numpy.unravel_index() takes a shape and a flat index into an array, and returns the tuple that represents that index in the array. Is there an inverse? I can compute it by hand, but this seems like it must be a built-in function somewhere...

Answer 1

Since numpy 1.6.0 (May 2011) there is a built-in NumPy function ravel_multi_index

Converts a tuple of index arrays into an array of flat indices, applying boundary modes to the multi-index.

(This is also mentioned in a comment by user Bi Rico but should really appear as an answer)

Answer 2

This works:

def ravel_index(pos, shape):
    res = 0
    acc = 1
    for pi, si in zip(reversed(pos), reversed(shape)):
        res += pi * acc
        acc *= si
    return res