import an array in python

Question

How can I import an array to python  numpy arry  from a file and that way the file must be written if it doesn t already exist   For example  save out a matrix to a file then load it back

User · Answer

In Python  Storing a bare python list as a numpy array and then saving it out to file  then loading it back  and converting it back to a list takes some conversion tricks   The confusion is because python lists are not at all the same thing as numpy arrays   import numpy as np foods     grape    cherry    mango   filename      outfile dat npy  np save filename  np array foods   z   np load filename  tolist   print  z is      str z     This prints   z is    grape    cherry    mango     Which is stored on disk as the filename  outfile dat npy  The important methods here are the tolist   and np array      conversion functions

User · Answer

Have a look at SciPy cookbook  It should give you an idea of some basic methods to import  export data   If you save load the files from your own Python programs  you may also want to consider the Pickle module  or cPickle

User · Answer

Checkout the entry on the numpy example list  Here is the entry on  loadtxt     gt  gt  gt  from numpy import    gt  gt  gt   gt  gt  gt  data   loadtxt  myfile txt                           myfile txt contains 4 columns of numbers  gt  gt  gt  t z   data   0   data   3                            data is 2D numpy array  gt  gt  gt   gt  gt  gt  t x y z   loadtxt  myfile txt   unpack True                     to unpack all columns  gt  gt  gt  t z   loadtxt  myfile txt   usecols    0 3   unpack True        to select just a few columns  gt  gt  gt  data   loadtxt  myfile txt   skiprows   7                       to skip 7 rows from top of file  gt  gt  gt  data   loadtxt  myfile txt   comments                           use     as comment char instead of      gt  gt  gt  data   loadtxt  myfile txt   delimiter                          use     as column separator instead of whitespace  gt  gt  gt  data   loadtxt  myfile txt   dtype   int                        file contains integers instead of floats

User · Answer

Another option is numpy genfromtxt  e g   import numpy as np data   np genfromtxt  myfile dat  delimiter        This will make data a numpy array with as many rows and columns as are in your file

User · Answer

I know the question is old  but I think this might be good as a reference for people with similar questions   If you want to load data from an ASCII text file  which has the benefit or being more or less human-readable and easy to parse in other software   numpy loadtxt is probably what you want     http   docs scipy org doc numpy reference generated numpy loadtxt html   If you just want to quickly save and load numpy arrays matrices to and from a file  take a look at numpy save and numpy load    http   docs scipy org doc numpy reference generated numpy save html http   docs scipy org doc numpy reference generated numpy load html

[python] import an array in python

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