Python: Finding corresponding indices for an intersection of two lists

python indices set-intersection
user1620716 picture user1620716 · Sep 24, 2012 · Viewed 8.6k times · Source

This is somewhat related to a question I asked not too long ago today. I am taking the intersection of two lists as follows:

    inter = set(NNSRCfile['datetimenew']).intersection(catdate)

The two components that I am taking the intersection of belong to two lengthy lists. Is it possible to get the indices of the intersected values? (The indices of the original lists that is).

I'm not quite sure where to start with this one.

Any help is greatly appreciated!

Answer

mgilson picture mgilson · Sep 24, 2012

I would create a dictionary to hold the original indices:

ind_dict = dict((k,i) for i,k in enumerate(NNSRCfile['datetimenew']))

Now, build your sets as before:

inter = set(ind_dict).intersection(catdate)

Now, to get a list of indices:

indices = [ ind_dict[x] for x in inter ]

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