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

Brett Olsen brett.olsen@gmail....
Tue Aug 2 10:09:18 CDT 2011

On Tue, Aug 2, 2011 at 9:44 AM, Jeremy Conlin <jlconlin@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)
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)
array([  3.20000000e+04,   7.89131000e-01,   8.05999000e-03,

In [9]: input.close()

If you're reading from a file you can replace the StringIO objects
with file objects.


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