[Numpy-discussion] setmember1d: docstring vs. code

Charles R Harris charlesr.harris@gmail....
Sat Mar 10 16:16:35 CST 2007


On 3/10/07, Robert Kern <robert.kern@gmail.com> wrote:
>
> Jouni K. Seppänen wrote:
>
> > I think that either the docstring (and the book) should be corrected
> > to mention the assumption, or the code should be made to work in the
> > arbitrary case.
>
> This is the current docstring:
>
> In [2]: setmember1d?
> Type:           function
> Base Class:     <type 'function'>
> Namespace:      Interactive
> File:
> /Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages/numpy-
> 1.0.2.dev3569-py2.5-macosx-10.3-fat.egg/numpy/lib/arraysetops.py
> Definition:     setmember1d(ar1, ar2)
> Docstring:
>     Return a boolean array of shape of ar1 containing True where the
> elements
>     of ar1 are in ar2 and False otherwise.
>
>     Use unique1d() to generate arrays with only unique elements to use as
> inputs
>     to this function.
>
>     :Parameters:
>       - `ar1` : array
>       - `ar2` : array
>
>     :Returns:
>       - `mask` : bool array
>         The values ar1[mask] are in ar2.
>
>     :See also:
>       numpy.lib.arraysetops has a number of other functions for performing
> set
>       operations on arrays.
>
> > I would prefer the latter choice (but perhaps the
> > current code has some advantages).
>
> Well, it has the advantage of existing. If you have an implementation that
> is
> just as efficient, but works for general arrays, I'd love to see it.


Well, the version I posted awhile back works for general arrays. How
efficient it is compared to the current version I haven't investigated. For
reference, here it is again.

def ismember(ar1, ar2) :
    a = sort(ar2)
    il = a.searchsorted(ar1, side='left')
    ir = a.searchsorted(ar1, side='right')
    return ir != il


Chuck
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