[Numpy-discussion] Get the index of a comparison of two lists

FRENK Andreas Andreas.FRENK at 3ds.com
Fri Feb 11 09:01:08 EST 2011


I need to create a construct that returns the index of entries of the first list, if values in the first and second list are equal.

valA = [1,2,3,4,20,21,22,23,24]
valB = [1,2,3,4,  5,21,22,23]
The correct solution is: [0,1,2,3,5,6,7]

A potential loop can be:
for j,a in enumerate(valA):
    if a in valB:

Please note, valA can have entries like [1,10000000,1000000001,.....], i.e. it can be very sparse.
I also thought about using bincount, but due to the sparse nature the return values from bincount would allocate too much memory.

Any idea how to do it fast using numpy?


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