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

[FRENK Andreas]

Hi,

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.

Take
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:
takeList=[]
for j,a in enumerate(valA):
    if a in valB:
        takeList.append(j)


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?

Thanks,
Andreas

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