[Numpy-discussion] extract elements of an array that are contained in another array?

[Ning Sean]

Hi, I want to extract elements of an array (say, a) that are contained in
another array (say, b). That is, if a=array([1,1,2,3,3,4]), b=array([1,4]),
then I want array([1,1,4]).

I did the following but the speed is very slow (maybe because a is very
long):

c=array([])
for x in b:
   c=append(c,a[a==x])

any way to speed it up?

Thanks!
-Ning
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