[Numpy-discussion] searchsorted for exact matches, not preserving order
Andrew Jaffe
a.h.jaffe@gmail....
Fri Sep 11 10:24:11 CDT 2009
Dear all,
I've got two (integer) arrays, and I want to find the indices in the
first one that have entries in the second. I.E. I want all idx s.t.
there exists a j with a[idx]=b[j]. Here is my current implementation
(with a = pixnums, b=surveypix)
import numpy as np
def matchPix(pixnums, surveypix):
spix = np.sort(surveypix)
### returns a list of indices into spix to keep spix sorted when
inserting pixnums
ss = np.searchsorted(spix, pixnums)
ss[ss==len(spix)] = 0 ## if any of the pixnums are > max(spix)
### now need to extract the actual matches
idxs = [i for (i,s) in enumerate(ss) if pixnums[i]==spix[s]]
return np.asarray(idxs)
This works, and is pretty efficient, but to me this actually seems like
a more common task than searchsorted itself; is there a simpler, more
numpyish way to do this?
Andrew
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