Assignment will never change the data-type of an already allocated array. So,
x['f2'] = y will try to convert the array to 'S10'.
On my system I get:
array([(1, 2.0, 'Hello'), (2, 3.0, 'World')],
dtype=[('f0', '<i4'), ('f1', '<f4'), ('f2', '|S10')])
which is what I would expect.
If you want to change the data, then create a new data-type:
x2 = np.zeros((2,),dtype=('i4,f4,O'))
x2[:] = [(1,2.,'Hello'), (2,3.,'World')]
-Travis
On Sep 22, 2010, at 2:04 AM, keekychen.shared wrote:
> Dear All,
>
> See below code pls,
>
> import sicpy
> import numpy as np
>
> x = np.zeros((2,),dtype=('i4,f4,a10'))
> x[:] = [(1,2.,'Hello'),(2,3.,"World")]
>
> y = x['f2']
> #array(['Hello', 'World'],
> dtype='|S10')
>
> x['f2'] = y
> x
> #array([(1, 2.0, 'Hello'), (2, 3.0, 'World')],
> dtype=[('f0', '<i4'), ('f1', '<f4'), ('f2', '|S10')])
>
> y = y.astype('object')
> y
> array([Hello, World], dtype=object)
>
>
> x['f2'] = y
> array([(1, 2.0, 'HellWorld'), (2, 3.0, '\x00\x00\x00\x00\x00\x00\x18')],
> dtype=[('f0', '<i4'), ('f1', '<f4'), ('f2', '|S10')])
>
> ##here comes the problem: the f2 col type has not been changed and the
> data is not I wanted...
> ----------------------------------------------------------------------------
>
> here is why I need using this:
> suppose I have a datasource, csv, sql based db or what ever look like this:
>
> 1, 2.0, 'Hello'
> 2, 3.0, 'World'
> 3, 2.0, 'other string'
>
> I want to read them to a numpy array and process it's columns, it has no
> problem for processing the float or int type but string.
> After reading the manual and found the object dtype may store variable
> string then I want to exact the string col into an new array, try to
> process it then store back to the numpy "matrix" then store it back to
> the data source.
>
> May I know how I can do that? I do not care performance now.
>
>
> Thanks for any hints
>
> Rgs,
>
> KC
>
>
>
>
>
>
>
> _______________________________________________
> NumPy-Discussion mailing list
> [email protected]
> http://mail.scipy.org/mailman/listinfo/numpy-discussion
---
Travis Oliphant
Enthought, Inc.
[email protected]
1-512-536-1057
http://www.enthought.com
_______________________________________________
NumPy-Discussion mailing list
[email protected]
http://mail.scipy.org/mailman/listinfo/numpy-discussion
