[Numpy-discussion] list dtype?

Mark Wendell mark.wendell@gmail....
Sun Jul 19 17:59:52 CDT 2009


Excellent! I guess I was over-thinking it.

Many thanks.
Mark

On Sun, Jul 19, 2009 at 4:50 PM, David Goldsmith<d_l_goldsmith@yahoo.com> wrote:
>
> Robert'll correct me if I'm wrong, but I think what he meant is that all you have to do is:
>
> array_of_lists = numpy.empty(<shape tuple>, dtype=object)
>
> and you'll be able to fill array_of_lists with whatever you want:
>
>>>> aol = np.empty((2,2),dtype=object)
>>>> aol[:,:] = [[[1, 2, 3], ['a','b','c']], [[(), (), ()], [{}, {}, {}]]]
>>>> aol
> array([[[1, 2, 3], ['a', 'b', 'c']],
>       [[(), (), ()], [{}, {}, {}]]], dtype=object)
>
> However, you do have to specify the shape ahead of time:
>
>>>> aol = np.empty((),dtype=object)
>>>> aol[:,:] = [list([5, 6, 7]),list(['a', 'b', 'c'])]
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
> IndexError: 0-d arrays can't be indexed.
>>>> aol.shape = (2,2)
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
> ValueError: total size of new array must be unchanged
>
> (Of course, if you need to change its size and shape, you can always instantiate a new array, initializing the "old" portion of it w/ the existing array and filling in the rest w/ the new values.)
>
> DG
>
> --- On Sun, 7/19/09, Mark Wendell <mark.wendell@gmail.com> wrote:
>
>> From: Mark Wendell <mark.wendell@gmail.com>
>> Subject: Re: [Numpy-discussion] list dtype?
>> To: "Discussion of Numerical Python" <numpy-discussion@scipy.org>
>> Date: Sunday, July 19, 2009, 3:19 PM
>> Sorry for being a newbie about it,
>> but could you provide an example?
>>
>> I was able to do this:
>>
>> d = np.dtype( {'names':['mylist'], 'formats':[np.object]})
>> but I'm not sure if that's the correct way to produce a
>> python list-type dtype.
>>
>> Further, how do I then define a new array with that as a
>> dtype?
>>
>> When I do this:
>> a = np.array( (5,5), dtype = d)
>> I get the error:
>> ValueError: size of tuple must match number of fields.
>>
>>
>> Any help appreciated. Thanks!
>> Mark
>>
>> On Sun, Jul 19, 2009 at 2:37 PM, Robert Kern<robert.kern@gmail.com>
>> wrote:
>> > On Sun, Jul 19, 2009 at 11:22, Mark Wendell<mark.wendell@gmail.com>
>> wrote:
>> >> Is it possible to create a dtype that is a list of
>> arbitrary length?
>> >
>> > Use the object dtype.
>> >
>> > --
>> > Robert Kern
>> >
>> > "I have come to believe that the whole world is an
>> enigma, a harmless
>> > enigma that is made terrible by our own mad attempt to
>> interpret it as
>> > though it had an underlying truth."
>> >  -- Umberto Eco
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>> > http://mail.scipy.org/mailman/listinfo/numpy-discussion
>> >
>>
>>
>>
>> --
>> --
>> Mark Wendell
>> "I guess songs are just interesting things to do with the
>> air." Tom Waits
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>
>
>
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-- 
--
Mark Wendell


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