numpy-discussion

[Numpy-discussion] array of tuples

[Travis N. V. <tr...@en...>]

I'd like to construct an array of tuples and I'm not sure how (without 
looping).  Is there a quick way to do this with dtype?

I've tried:

 >>> import numpy
 >>> x = [(1,2,3),(4,5,6)]
 >>> numpy.array(x)
array([[1, 2, 3],
       [4, 5, 6]])
 >>> numpy.array(x, dtype='p')
array([[1, 2, 3],
       [4, 5, 6]])
 >>> numpy.array(x, dtype='O')
array([[1, 2, 3],
       [4, 5, 6]], dtype=object)

Thanks,

Travis

Re: [Numpy-discussion] array of tuples

[Christopher B. <Chr...@no...>]

Travis N. Vaught wrote:
> I'd like to construct an array of tuples and I'm not sure how (without 
> looping). 

Is this what you want?

 >>> import numpy as N
 >>> a = N.empty((2,),dtype=object)
 >>> a[:] = [(1,2,3),(4,5,6)]
 >>> a
array([(1, 2, 3), (4, 5, 6)], dtype=object)
 >>> a.shape
(2,)

By the way, I notice that the object dtype is not in the numpy 
namespace. While this mikes sense, as it's part of python, I keep 
getting confused because I do need to use numpy-specific dtypes for 
other things. I never use import *, so it might be a good idea to put 
the standard objects dtypes in the numpy namespace too. Or maybe not, 
just thinking out loud.

Note: PyObject is there, but isn't that a deprecated Numeric name?

-Chris


-- 
Christopher Barker, Ph.D.
Oceanographer
                                     		
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Chr...@no...

Re: [Numpy-discussion] array of tuples

[David M. C. <co...@ph...>]

On Tue, 06 Jun 2006 13:21:56 -0700
Christopher Barker <Chr...@no...> wrote:

> 
> 
> Travis N. Vaught wrote:
> > I'd like to construct an array of tuples and I'm not sure how (without 
> > looping). 
> 
> Is this what you want?
> 
>  >>> import numpy as N
>  >>> a = N.empty((2,),dtype=object)
>  >>> a[:] = [(1,2,3),(4,5,6)]
>  >>> a
> array([(1, 2, 3), (4, 5, 6)], dtype=object)
>  >>> a.shape
> (2,)
> 
> By the way, I notice that the object dtype is not in the numpy 
> namespace. While this mikes sense, as it's part of python, I keep 
> getting confused because I do need to use numpy-specific dtypes for 
> other things. I never use import *, so it might be a good idea to put 
> the standard objects dtypes in the numpy namespace too. Or maybe not, 
> just thinking out loud.

None of the Python types are (int, float, etc.). For one reason, various
Python checkers complain about overwriting a builtin type, and plus, I
think it's messy and a potential for bugs. numpy takes those as convenience
types, and converts them to the appropriate dtype. If you want the dtype
used, it's spelled with an appended _.

So in this case you'd want dtype=N.object_. N.object0 works too.

-- 
|>|\/|<
/--------------------------------------------------------------------------\
|David M. Cooke                      http://arbutus.physics.mcmaster.ca/dmc/
|co...@ph...

Re: [Numpy-discussion] array of tuples

[Christopher B. <Chr...@no...>]

David M. Cooke wrote:
> If you want the dtype
> used, it's spelled with an appended _.
> 
> So in this case you'd want dtype=N.object_. N.object0 works too.

That will work, thanks. But what does object0 mean?

-Chris




-- 
Christopher Barker, Ph.D.
Oceanographer
                                     		
NOAA/OR&R/HAZMAT         (206) 526-6959   voice
7600 Sand Point Way NE   (206) 526-6329   fax
Seattle, WA  98115       (206) 526-6317   main reception

Chr...@no...

Re: [Numpy-discussion] array of tuples

[David M. C. <co...@ph...>]

On Tue, 06 Jun 2006 14:15:14 -0700
Christopher Barker <Chr...@no...> wrote:

> David M. Cooke wrote:
> > If you want the dtype
> > used, it's spelled with an appended _.
> > 
> > So in this case you'd want dtype=N.object_. N.object0 works too.
> 
> That will work, thanks. But what does object0 mean?

I think it's "type object, default size". It's a holdover from Numeric. int0,
for instance, is the same as int_ (= int64 on my 64-bit box, for instance).

-- 
|>|\/|<
/--------------------------------------------------------------------------\
|David M. Cooke                      http://arbutus.physics.mcmaster.ca/dmc/
|co...@ph...

Re: [Numpy-discussion] array of tuples

[Stefan v. d. W. <st...@su...>]

On Tue, Jun 06, 2006 at 01:05:43PM -0500, Travis N. Vaught wrote:
> looping).  Is there a quick way to do this with dtype?
>=20
> I've tried:
>=20
>  >>> import numpy
>  >>> x =3D [(1,2,3),(4,5,6)]
>  >>> numpy.array(x)
> array([[1, 2, 3],
>        [4, 5, 6]])
>  >>> numpy.array(x, dtype=3D'p')
> array([[1, 2, 3],
>        [4, 5, 6]])
>  >>> numpy.array(x, dtype=3D'O')
> array([[1, 2, 3],
>        [4, 5, 6]], dtype=3Dobject)

It works if you pre-allocate the array:

In [18]: x =3D [(1,2),(3,4)]

In [19]: z =3D N.empty(len(x),dtype=3D'O')

In [20]: z[:] =3D x

In [21]: z
Out[21]: array([(1, 2), (3, 4)], dtype=3Dobject)

Regards
St=E9fan

Re: [Numpy-discussion] array of tuples

[Christopher B. <Chr...@no...>]

Stefan van der Walt wrote:

> In [19]: z = N.empty(len(x),dtype='O')

Which brings up:

What is the "preferred" way to refer to types? String typecode or object?

-Chris

-- 
Christopher Barker, Ph.D.
Oceanographer
                                     		
NOAA/OR&R/HAZMAT         (206) 526-6959   voice
7600 Sand Point Way NE   (206) 526-6329   fax
Seattle, WA  98115       (206) 526-6317   main reception

Chr...@no...

Re: [Numpy-discussion] array of tuples

[Robert K. <rob...@gm...>]

Christopher Barker wrote:
> Stefan van der Walt wrote:
> 
>>In [19]: z = N.empty(len(x),dtype='O')
> 
> Which brings up:
> 
> What is the "preferred" way to refer to types? String typecode or object?

Object! The string typecodes are for backwards compatibility only.

-- 
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