On Thu, Jun 4, 2009 at 11:19 AM, Alan G Isaac <ais...@american.edu> wrote: > On 6/4/2009 10:50 AM josef.p...@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.)
intersect1d is the intersection between sets (which are stored as arrays), just like in the mathematical definition the two sets only have unique elements intersect1d_nu is the intersection between two arrays which can have repeated elements. The result is a set, i.e. unique elements, stored as an array same for setmember1d, setmember1d_nu so postfix `_nu` only means that this function also works if the two arrays are not really sets, i.e. are not required to have unique elements to make sense. intersect1d should throw a domain error if you give it arrays with non-unique elements, which is not done for speed reasons > Cheers, > Alan Isaac _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
