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17

Is there a way to dump a NumPy array into a CSV file? I have a 2D NumPy array and need to dump it in human-readable format.

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3 Answers 3

up vote 186 down vote accepted 
import numpy
a = numpy.asarray([ [1,2,3], [4,5,6], [7,8,9] ])
numpy.savetxt("foo.csv", a, delimiter=",")
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is this preferred over looping through the array by dimension? I'm guessing so. – Ehtesh Choudhury May 21 '11 at 10:13
    
The array is an ndarray. I hope it adds up. – Dexter May 21 '11 at 16:53
1  
It did. Thanks! – Dexter May 22 '11 at 11:00
14  
you can also change the format of each figure with the fmt keyword. default is '%.18e', this can be hard to read, you can use '%.3e' so only 3 decimals are shown. – Andrea Zonca May 22 '11 at 17:25
1  
Andrea, Yes I used %10.5f. It was pretty convenient. – Dexter May 23 '11 at 9:47
up vote 8 down vote

savetxt may just be sufficient.

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up vote 2 down vote

tofile is a convenient function to do this:

import numpy as np
a = np.asarray([ [1,2,3], [4,5,6], [7,8,9] ])
a.tofile('foo.csv',sep=',',format='%10.5f')

The man page has some useful notes:

This is a convenience function for quick storage of array data. Information on endianness and precision is lost, so this method is not a good choice for files intended to archive data or transport data between machines with different endianness. Some of these problems can be overcome by outputting the data as text files, at the expense of speed and file size.

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