Using a for loop for extracting a range of columns with astropy in python

Question

I have the following file:

rowname1     0.0019      0.0142     -0.0258     -0.0058     -0.0097      
rowname2     0.0001      0.0168     -0.0268     -0.0063     -0.0072

and I would like to extract the columns from 2nd (i.e. avoiding the rownames column) to xth. So far I am using the astropy module ascii.read function; if I e.g. set x = 3:

from astropy.io import ascii
x = 3
evec = ascii.read('file', include_names=['col'[i] for i in xrange(2,x)])
print evec

it just returns

<No columns>

How should the for loop be in order to work properly?

Thank you!

It seems to me astropy expects column names for reading tables from ASCII files. C.f.: http://docs.astropy.org/en/stable/io/ascii/ — Martin Krämer, May 08 '17 at 12:36
If you run: from astropy.io import ascii evec = ascii.read('file', include_names=['col2','col3']) print evec you get the two first columns — Miguel, May 08 '17 at 12:42
Ah, I see. the problem is you are selecting the second character of 'col' with 'col'[i], while you actually want to concatenate. — Martin Krämer, May 08 '17 at 12:44
And consider that the upper end of the range is non-inclusive, i.e. if you want to include x put xrange(2, x+1). — Martin Krämer, May 08 '17 at 12:46

score 1 · Accepted Answer · answered May 08 '17 at 12:48

You have a bug in include_names, i.e. you select the 2nd character of 'col' and do not concatenate the number to the string.

Just replace it with:

evec = ascii.read('file', include_names = ['col' + str(i) for i in xrange(2,x)])

Also consider that the second parameter of xrange is not included; so if you want to include 3 in your example use xrange(2,x+1).

Using a for loop for extracting a range of columns with astropy in python

1 Answers1