[Numpy-discussion] Finding many ways to incorrectly create a numpy array. Please advice

[Jeremy Conlin]

On Tue, Aug 2, 2011 at 9:09 AM, Brett Olsen <brett.olsen at gmail.com> wrote:
> On Tue, Aug 2, 2011 at 9:44 AM, Jeremy Conlin <jlconlin at gmail.com> wrote:
>> I am trying to create a numpy array from some text I'm reading from a
>> file. Ideally, I'd like to create a structured array with the first
>> element as an int and the remaining as floats. I'm currently
>> unsuccessful in my attempts. I've copied a simple script below that
>> shows what I've done and the wrong output. Can someone please show me
>> what is happening?
>>
>> I'm using numpy version 1.5.1 under Python 2.7.1 on a Mac running Snow Leopard.
>>
>> Thanks,
>> Jeremy
>
> I'd use numpy.loadtxt:
>
> In [1]: import numpy, StringIO
>
> In [2]: l = '      32000  7.89131E-01  8.05999E-03  3.88222E+03'
>
> In [3]: tfc_dtype = numpy.dtype([('nps', 'u8'), ('t', 'f8'), ('e',
> 'f8'), ('fom', 'f8')])
>
> In [4]: input = StringIO.StringIO(l)
>
> In [5]: numpy.loadtxt(input, dtype=tfc_dtype)
> Out[5]:
> array((32000L, 0.78913100000000003, 0.0080599899999999995, 3882.2199999999998),
>      dtype=[('nps', '<u8'), ('t', '<f8'), ('e', '<f8'), ('fom', '<f8')])
>
> In [6]: input.close()
>
> In [7]: input = StringIO.StringIO(l)
>
> In [8]: numpy.loadtxt(input)
> Out[8]:
> array([  3.20000000e+04,   7.89131000e-01,   8.05999000e-03,
>         3.88222000e+03])
>
> In [9]: input.close()
>
> If you're reading from a file you can replace the StringIO objects
> with file objects.

Thanks, Brett. Using StringIO and numpy.loadtxt worked great. I'm
still curious why what I was doing didn't work. Everything I can see
indicates it should work.

Jeremy