How to save numpy ndarray as .csv file?

Question

I created a numpy array as follows:

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

The values in ab are shown below:

array([(u'NAME_1',  0.1234), (u'NAME_2',  0.5678), (u'NAME_3',  0.9123)],
      dtype=[('var1', '<U6'), ('var2', '<f8')])

When I try to save ab as a .csv file using savetxt() command,

np.savetxt('D:\test.csv',ab,delimiter=',')

I get below error

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-66-a71fd201aefe> in <module>()
----> 1 np.savetxt('D:\Azim\JF-Mapping-workflow-CRM\Backup\delete.csv',ab,delimiter=',')

c:\python27\lib\site-packages\numpy\lib\npyio.pyc in savetxt(fname, X, fmt, delimiter, newline, header, footer, comments)
   1256                     raise TypeError("Mismatch between array dtype ('%s') and "
   1257                                     "format specifier ('%s')"
-> 1258                                     % (str(X.dtype), format))
   1259         if len(footer) > 0:
   1260             footer = footer.replace('\n', '\n' + comments)

TypeError: Mismatch between array dtype ('[('var1', '<U6'), ('var2', '<f8')]') and format specifier ('%.18e,%.18e')

A general case: stackoverflow.com/questions/6081008/…

Anton Tarasenko
– Anton Tarasenko

2018-11-22 15:54:33 +00:00
Commented Nov 22, 2018 at 15:54 — Anton Tarasenko
– Anton Tarasenko, Commented Nov 22, 2018 at 15:54
@Anton, thanks for sharing additional information.

StatguyUser
– StatguyUser

2018-11-22 16:19:42 +00:00
Commented Nov 22, 2018 at 16:19 — StatguyUser
– StatguyUser, Commented Nov 22, 2018 at 16:19

Dror Paz · Accepted Answer · 2018-02-05 12:18:54Z

15

Your array include strings, but np default formatting is for floats.

Try manually setting the format:

np.savetxt(r'g:\test.csv',ab,delimiter=',', fmt=('%s, %f'))

answered Feb 5, 2018 at 12:18

Dror Paz

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1 Comment

StatguyUser Over a year ago

Thanks for your help. I just tested your code, its not working either. Edit: It's working perfectly fine.

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