[Numpy-discussion] Creating a 1-d structured array

[Robert Kern]

On Fri, May 13, 2011 at 09:58, Bruce Southey <bsouthey at gmail.com> wrote:
> Hi,
> How do you create a 'single' structured array using np.array()?
> Basically I am attempting to do something like this that does not work:
> a=np.array([1,2, 3,4, 5,6], dtype=np.dtype([('foo', int)]))
>
> I realize that this is essentially redundant as if A is an 1-d array
> then a structured array with a named field 'foo' is the same thing - A
> would be A['foo'], just shorter.
>
> So if that is valid then a clearer error message is required to indicate
> this and provide the suitable error message to address ticket 1264
> (http://projects.scipy.org/numpy/ticket/1264).
>
> $ python
> Python 2.7 (r27:82500, Sep 16 2010, 18:02:00)
> [GCC 4.5.1 20100907 (Red Hat 4.5.1-3)] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
>  >>> import numpy as np
>  >>> a=np.array([1,2, 3,4, 5,6], dtype=np.dtype([('foo', int)]))
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: expected a readable buffer object
>  >>> np.array([(1,2), (3,4), (5,6)], dtype=np.dtype([('foo', int),
> ('foo2', int)]))
> array([(1, 2), (3, 4), (5, 6)],
>       dtype=[('foo', '<i8'), ('foo2', '<i8')])
>  >>> a=np.array([(1), (3), (5)], dtype=np.dtype([('foo', int)]))
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: expected a readable buffer object

You are missing the commas:

[~]
|12> a=np.array([(1,), (3,), (5,)], dtype=np.dtype([('foo', int)]))

[~]
|13> a
array([(1,), (3,), (5,)],
      dtype=[('foo', '<i4')])


-- 
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