How to use python numpy savetxt to write strings and float number to an ASCII file

Question

I have a set of lists that contain both strings and float numbers  such as   import numpy as num  NAMES    num array   NAME 1    NAME 2    NAME 3    FLOATS   num array   0 5      0 2       0 3         DAT    num column stack  NAMES  FLOATS     I want to stack these two lists together and write them to a text file in the form of columns  therefore  I want to use numpy savetxt  if possible  to do this   num savetxt  test txt   DAT  delimiter         When I do this  I get the following error    gt  gt  gt  num savetxt  test txt   DAT  delimiter       Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   Library Python 2 7 site-packages numpy-1 8 0 dev 9597b1f 20120920-py2 7-macosx-10 8-x86 64 egg numpy lib npyio py   line 1047  in savetxt     fh write asbytes format   tuple row    newline   TypeError  float argument required  not numpy string    The ideal output file would look like   NAME 1    0 5 NAME 2    0 2 NAME 3    0 3   How can I write both strings and float numbers to a text file  possibly avoiding using csv   I want to make if readable for other people    Is there another way of doing this instead of using numpy savetxt

User · Answer

The currently accepted answer does not actually address the question, which asks how to save lists that contain both strings and float numbers. For completeness I provide a fully working example, which is based, with some modifications, on the link given in @joris comment.

import numpy as np

names  = np.array(['NAME_1', 'NAME_2', 'NAME_3'])
floats = np.array([ 0.1234 ,  0.5678 ,  0.9123 ])

ab = np.zeros(names.size, dtype=[('var1', 'U6'), ('var2', float)])
ab['var1'] = names
ab['var2'] = floats

np.savetxt('test.txt', ab, fmt="%10s %10.3f")

Update: This example also works properly in Python 3 by using the 'U6' Unicode string dtype, when creating the ab structured array, instead of the 'S6' byte string. The latter dtype would work in Python 2.7, but would write strings like b'NAME_1' in Python 3.

User · Answer

You have to specify the format  fmt  of you data in savetxt  in this case as a string   s    num savetxt  test txt   DAT  delimiter      fmt   s      The default format is a float  that is the reason it was expecting a float instead of a string and explains the error message

[python] How to use python numpy.savetxt to write strings and float number to an ASCII file?

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