sort array, apply rearrangement to second

[Alf P. Steinbach]

* Victor Eijkhout:
> I have two arrays, made with numpy. The first one has values that I want
> to use as sorting keys; the second one needs to be sorted by those keys.
> Obviously I could turn them into a dictionary  of pairs and sort by the
> first member, but I think that's not very efficient, at least in space,
> and this needs to be done as efficiently as possible.
> 
> I could use a hand.

Just do the pairing, but in a 'list', not a dictionary (a dictionary is 
unordered and can't be sorted). You need to keep track of which keys belong to 
which values anyway. And anything in Python is a reference: you're not copying 
the data by creating the pairs. That is, the space overhead is proportional to 
the number of items but is independent of the data size of each item.


Cheers & hth.,

- Alf