[Numpy-discussion] assign a float number to a member of integer array always return integer
Chris Barker
chris.barker at noaa.gov
Tue May 22 12:18:45 EDT 2012
On Tue, May 22, 2012 at 6:33 AM, Chao YUE <chaoyuejoy at gmail.com> wrote:
> Just in case some one didn't know this. Assign a float number to an integer
> array element will always return integer.
right -- numpy arrays are typed -- that's one of the points of them --
you wouldn't want the entire array up-cast with a single assignment --
particularly since there are only python literals for a subset of the
numpy types.
> so I would always do this if I expected a transfer from integer to float?
> In [18]: b=a.astype(float)
yes -- but that's an odd way of thinking about -- what you want to do
is think about what type you need your array to be before you create
it, then create it the way you need it:
In [87]: np.arange(5, dtype=np.float)
Out[87]: array([ 0., 1., 2., 3., 4.])
or better:
In [91]: np.linspace(0,5,6)
Out[91]: array([ 0., 1., 2., 3., 4., 5.])
note that most (all?) numpy array constructors take a "dtype" argument.
-Chris
> In [19]: b
> Out[19]: array([ 2., 4., 6., 8., 10.])
>
> In [20]: b[1]=4.5
>
> In [21]: b
> Out[21]: array([ 2. , 4.5, 6. , 8. , 10. ])
>
> thanks et cheers,
>
> Chao
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