Adding a field to a structured numpy array (2)

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Adding a field to a structured numpy array (2)

I know there was already a question about this topic (cleanest way to add a field to a structured numpy array), see

Adding a field to a structured numpy array

but I have a question about the answer given there …

If you’re using numpy 1.3, there’s also numpy.lib.recfunctions.append_fields()

I still have numpy 1.3, but it doesn’t recognise this function, and I also didn’t find anything about it in the documentation of numpy. What happened with the function? Is there another function that can do the same?

Asked By: joris


Answer #1:

As far as documentation for the recfunctions, here it is:

If you can’t figure it out after reading that, then please provide some code samples (for instance, did you import numpy.lib.recfunctions?) and an error message or undesired result, so we can determine how to fix it.

Answered By: J. Taylor

Answer #2:

did you import?

from numpy.lib import recfunctions

recfunctions.append_fields(*your_args)  # base, names, data, ...

Seems like everything is working:

Python 2.6.6 (r266:84292, Sep 15 2010, 15:52:39) 
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy
>>> numpy.__version__
>>> from numpy.lib.recfunctions import append_fields
>>> append_fields
<function append_fields at 0x9e3e80c>
Answered By: dting

Answer #3:

Here is a concrete example how to use append_fields(..) (admittedly based on the other answers here):

import numpy as np
x = np.array(np.arange(0,10), dtype = [('x', float)])
y = np.array(np.arange(10,20), dtype = [('y', float)])

from numpy.lib.recfunctions import append_fields

z = append_fields(x, 'y', y)



will give

('x', 'y')

note that y in can also be ‘plain’ ndarray without column names:

y = np.arange(10,20)

or you can rename the column y to something else (even if y is a structured array with column names):

z = append_fields(x, 'p', y)

(tested in numpy 1.6.1)

Answered By: Andre Holzner

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