Dump a NumPy array into a csv file

Question

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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You can also do it with pure python without using any modules     format as a block of csv text to do whatever you want csv rows            format i  j  for i  j in array  csv text     n  join csv rows     write it to a file with open  file csv    w   as f      f write csv text

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If you want to save your numpy array  e g  your array   np array   1 2   3 4     to one cell  you could convert it first with your array tolist     Then save it the normal way to one cell  with delimiter     and the cell in the csv-file will look like this   1  2    2  4    Then you could restore your array like this  your array   np array ast literal eval cell string

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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    Note  This function does not produce multi-line csv files  it saves everything to one line

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Writing record arrays as CSV files with headers requires a bit more work  This example reads from a CSV file   example csv   and writes its contents to another CSV file  out csv   import numpy as np    Write an example CSV file with headers on first line with open  example csv    w   as fp      fp write      col1 col2 col3 1 100 1 string1 2 222 2 second string         Read it as a Numpy record array ar   np recfromcsv  example csv   print repr ar     rec array   1  100 1   string1     2  222 2   second string                  dtype    col1     lt i4      col2     lt f8      col3    S13        Write as a CSV file with headers on first line with open  out csv    w   as fp      fp write     join ar dtype names      n       np savetxt fp  ar    s         Note that the above example cannot handle values which are strings with commas  To always enclose non-numeric values within quotes  use the csv package  import csv  with open  out2 csv    wb   as fp      writer   csv writer fp  quoting csv QUOTE NONNUMERIC      writer writerow ar dtype names      writer writerows ar tolist

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You can use pandas  It does take some extra memory so it s not always possible  but it s very fast and easy to use   import pandas as pd  pd DataFrame np array  to csv  path to file csv     if you don t want a header or index  use to csv   path to file csv   header None  index None

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numpy savetxt saves an array to a text file   import numpy a   numpy asarray    1 2 3    4 5 6    7 8 9     numpy savetxt  foo csv   a  delimiter

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As already discussed  the best way to dump the array into a CSV file is by using  savetxt     method  However  there are certain things we should know to do it properly    For example  if you have a numpy array with dtype   np int32 as     narr   np array   1 2                     3 4                     5 6    dtype np int32    and want to save using savetxt as  np savetxt  values csv   narr  delimiter        It will store the data in floating point exponential format as  1 000000000000000000e 00 2 000000000000000000e 00 3 000000000000000000e 00 4 000000000000000000e 00 5 000000000000000000e 00 6 000000000000000000e 00   You will have to change the formatting by using a parameter called fmt as  np savetxt  values csv   narr  fmt   d   delimiter        to store data in its original format  Saving Data in Compressed gz format  Also  savetxt can be used for storing data in  gz compressed format which might be useful while transferring data over network    We just need to change the extension of the file as  gz and numpy will take care of everything automatically  np savetxt  values gz   narr  fmt   d   delimiter        Hope it helps

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if you want to write in column       for x in np nditer a T  order  C                 file write str x               file write   n     Here  a  is the name of numpy array and  file  is the variable to write in a file   If you want to write in row       writer  csv writer file  delimiter          for x in np nditer a T  order  C                 row append str x       writer writerow row

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I believe you can also accomplish this quite simply as follows    Convert Numpy array into a Pandas dataframe Save as CSV   e g   1         Libraries to import     import pandas as pd     import nump as np       N x N numpy array  dimensions dont matter      corr mat     your numpy array     my df   pd DataFrame corr mat    converting it to a pandas dataframe   e g   2        save as csv      my df to csv  foo csv   index False       foo  is the name you want to give                                              to csv file  Make sure to add   csv                                               after whatever name like in the code

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In Python we use csv writer   module to write data into csv files  This module is similar to the csv reader   module   import csv  person      SN    Person    DOB      1    John    18 1 1997      2    Marie   19 2 1998      3    Simon   20 3 1999      4    Erik    21 4 2000      5    Ana    22 5 2001     csv register dialect  myDialect   delimiter        quoting csv QUOTE NONE  skipinitialspace True   with open  dob csv    w   as f      writer   csv writer f  dialect  myDialect       for row in person         writer writerow row   f close     A delimiter is a string used to separate fields  The default value is comma

[python] Dump a NumPy array into a csv file

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