[Numpy-discussion] extract elements of an array that are contained in another array?
Alan G Isaac
aisaac at american.edu
Thu Jun 4 11:19:49 EDT 2009
On 6/4/2009 10:50 AM josef.pktd at gmail.com apparently wrote:
> intersect1d gives set intersection if both arrays have
> only unique elements (i.e. are sets). I thought the
> naming is pretty clear:
> intersect1d(a,b) set intersection if a and b with unique elements
> intersect1d_nu(a,b) set intersection if a and b with non-unique elements
> setmember1d(a,b) boolean index array for a of set intersection if a
> and b with unique elements
> setmember1d_nu(a,b) boolean index array for a of set intersection if
> a and b with non-unique elements
>>> a
array([1, 1, 2, 3, 3, 4])
>>> b
array([1, 4, 4, 4])
>>> np.intersect1d_nu(a,b)
array([1, 4])
That is, intersect1d_nu is the actual set intersection
function. (I.e., intersect1d and intersect1d_nu would most
naturally have swapped names.) That is why the appended _nu
will not communicate what was intended. (I.e.,
setmember1d_nu will not be a match for intersect1d_nu.)
Cheers,
Alan Isaac
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