[Numpy-discussion] Constant array of tuples

[Christopher Barker]

Frank Peacock wrote:
> Hello
> 
> I would like to know whether there is a simple way to construct a constant
> array of tuples:
> 
> How do I construct an array of size (width*height) where each element is
> (w,x,y,z)

Is this what you want?

a = np.empty((5,6), dtype=np.object)
 >>> for i in range(len(a.flat)):
...   a.flat[i] = (1,2,3,4)
...
 >>> a
array([[(1, 2, 3, 4), (1, 2, 3, 4), (1, 2, 3, 4), (1, 2, 3, 4),
         (1, 2, 3, 4), (1, 2, 3, 4)],
        [(1, 2, 3, 4), (1, 2, 3, 4), (1, 2, 3, 4), (1, 2, 3, 4),
         (1, 2, 3, 4), (1, 2, 3, 4)],
        [(1, 2, 3, 4), (1, 2, 3, 4), (1, 2, 3, 4), (1, 2, 3, 4),
         (1, 2, 3, 4), (1, 2, 3, 4)],
        [(1, 2, 3, 4), (1, 2, 3, 4), (1, 2, 3, 4), (1, 2, 3, 4),
         (1, 2, 3, 4), (1, 2, 3, 4)],
        [(1, 2, 3, 4), (1, 2, 3, 4), (1, 2, 3, 4), (1, 2, 3, 4),
         (1, 2, 3, 4), (1, 2, 3, 4)]], dtype=object)

Interestingly:

 >>> a[:,:] = (1,2,3,4)
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
ValueError: shape mismatch: objects cannot be broadcast to a single shape

Doesn't work - even though (1,2,3,4) is a tuple, which is a single object.

Anyway, I suspect that that's not really what you want, but rather, you 
might be looking for:

 >>> a = np.zeros((w,h,4), np.float)
 >>> a[:,:] = (1,2,3,4)
 >>> a
array([[[ 1.,  2.,  3.,  4.],
         [ 1.,  2.,  3.,  4.],
         [ 1.,  2.,  3.,  4.],
         [ 1.,  2.,  3.,  4.],
         [ 1.,  2.,  3.,  4.]],

        [[ 1.,  2.,  3.,  4.],
         [ 1.,  2.,  3.,  4.],
         [ 1.,  2.,  3.,  4.],
         [ 1.,  2.,  3.,  4.],
         [ 1.,  2.,  3.,  4.]],

        [[ 1.,  2.,  3.,  4.],
         [ 1.,  2.,  3.,  4.],
         [ 1.,  2.,  3.,  4.],
         [ 1.,  2.,  3.,  4.],
         [ 1.,  2.,  3.,  4.]]])


-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.Barker at noaa.gov