[Numpy-discussion] Inverted indices

Nicolas P. Rougier Nicolas.Rougier at inria.fr
Thu Aug 7 07:16:13 EDT 2014


I've a small problem for which I cannot find a solution and I'm quite sure there is an obvious one:

I've an array Z (any dtype) with some data.
I've a (sorted) array I (of integer, same size as Z) that tells me the  index of Z[i]  (if necessary, the index can be stored in Z).

Now, I have an arbitrary sequence S of indices (in the sense of I), how do I build the corresponding data ?

Here is a small example:

Z = [(0,0), (1,1), (2,2), (3,3), (4,4))
I  = [0, 20, 23, 24, 37]

S = [ 20,20,0,24]
-> Result should be [(1,1), (1,1), (0,0),(3,3)]

S = [15,15]
-> Wrong (15 not in I) but ideally, I would like this to be converted to [(0,0), (0,0)]

Any idea ?


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