On Sun, May 29, 2011 at 10:58 PM, Chris Barker <chris.bar...@noaa.gov>wrote:
> > On 5/28/2011 3:40 PM, Robert wrote:
> >> (myarray in mylist) turns into mylist.__contains__(myarray).
> >> Only the list object is ever checked for this method. There is no
> >> paired method myarray.__rcontains__(mylist) so there is nothing that
> >> numpy can override to make this operation do anything different from
> >> what lists normally do,
>
> however, numpy arrays should be able to override "in" be defining their
> own.__contains__ method, so you could do:
>
> something in an_array
>
> and get a useful, vectorized result.
>
> So I thought I'd see what currently happens when I try that:
>
> In [24]: a
> Out[24]: array([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11])
>
> In [25]: 3 in a
> Out[25]: True
>
> So the simple case works just like a list. But what If I want what the
> OP wants:
>
> In [26]: b
> Out[26]: array([3, 6, 4])
>
> In [27]: b in a
> Out[27]: False
>
> OK, so the full b array is not in a, and it doesn't "vectorize" it,
> either. But:
>
> In [29]: a
> Out[29]:
> array([[ 0, 1, 2],
> [ 3, 4, 5],
> [ 6, 7, 8],
> [ 9, 10, 11]])
>
> In [30]: b in a
> Out[30]: True
>
> HUH?
>
> I'm not sure by what definition we would say that b is contained in a.
>
> but maybe..
>
> In [41]: b
> Out[41]: array([ 4, 2, 345])
>
> In [42]: b in a
> Out[42]: False
>
> so it's "are all of the elements in b in a somewhere?" but only for 2-d
> arrays?
>
>
> So what does it mean?
>
FWIW, a short prelude on the theme seems quite promising, indeed:
In []: A
Out[]:
array([[0, 1, 2],
[3, 4, 5],
[6, 7, 8]])
In []: [0, 1, 2] in A
Out[]: True
In []: [0, 3, 6] in A
Out[]: True
In []: [0, 4, 8] in A
Out[]: True
In []: [8, 4, 0] in A
Out[]: True
In []: [2, 4, 6] in A
Out[]: True
In []: [6, 4, 2] in A
Out[]: True
In []: [3, 1, 5] in A
Out[]: True
In [1061]: [3, 1, 4] in A
Out[1061]: True
But
In []: [1, 2, 3] in A
Out[]: False
In []: [3, 2, 1] in A
Out[]: True
So, obviously the logic behind __contains__ is not so very straightforward.
Perhaps just a bug?
Regards,
eat
>
> The docstring is not helpful:
>
> In [58]: np.ndarray.__contains__?
> Type: wrapper_descriptor
> Base Class: <type 'wrapper_descriptor'>
> String Form: <slot wrapper '__contains__' of 'numpy.ndarray' objects>
> Namespace: Interactive
> Docstring:
> x.__contains__(y) <==> y in x
>
>
> If nothing useful, maybe it could provide a vectorized version of "in"
> for this sort of use case.
>
> -Chris
>
>
>
>
>
>
> --
> Christopher Barker, Ph.D.
> Oceanographer
>
> Emergency Response Division
> NOAA/NOS/OR&R (206) 526-6959 voice
> 7600 Sand Point Way NE (206) 526-6329 fax
> Seattle, WA 98115 (206) 526-6317 main reception
>
> chris.bar...@noaa.gov
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