Inserting columns in ndarray created using numpy.genfromtxt

Question

I created a ndarray from a txt file using numpy.genfromtxt. The txt file looks like:

2505000
10.316     1.936     0.025    0   15   0   0
10.316     1.937     0.028    0   15   0   0
10.316     1.943     0.028    0   15   0   0
10.316     1.954     0.022    0    9  58   0
10.316     1.955     0.026    0    9  58   0

I am running the reading the data with:

data = np.genfromtxt(fname,
                     skip_header =1,
                     dtype = [('X','f'),('Y','f'),('Z','f'),('V', 'i'),('T', 'i')],
                     usecols = (0,1,2,4,5))

I am now trying to duplicate the 4th column (the one I called V) and place it just after itself (before the last T column).

I know I can copy the column by doing data['V'], but how do I place this copy in between V and T (the 4th and 5th columns)? I had a look at numpy.insert, but I am not sure how to specify the index (the obj argument). I tried with numpy.insert(data_copy, data_copy['T'],data_copy['V']) with no luck (I received IndexError: index 61 is out of bounds for size 20).

You have to make a new dtype with the added field, and copy values by field name from the original array to the new one. — hpaulj
– hpaulj, Commented Nov 30, 2016 at 15:57
Look at from numpy.lib import recfunctions. stackoverflow.com/a/27952861/901925 — hpaulj
– hpaulj, Commented Nov 30, 2016 at 16:02
@hpaulj thanks, I solved by combining recfunctions.append_fields and recfunctions.drop_fields, although I cannot specify an insert position. If no other solution comes up, and you would like to turn your comment to answer, I would be happy to accept it. — umbe1987
– umbe1987, Commented Nov 30, 2016 at 16:32

Community · Accepted Answer · 2017-05-23 12:08:43Z

1

You have to make a new dtype with the added field, and copy values by field name from the original array to the new one.

recfunctions has functions to do this (and related actions):

 from numpy.lib import recfunctions

numpy dtype error - (structured array creation)

edited May 23, 2017 at 12:08

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answered Nov 30, 2016 at 18:11

hpaulj

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