I want to store more than one 2d arrays in file using python

Question

I am using python 2.7. I tried to store 2d arrays in file, but it stored only recent value. Suppose if I enter values for 3 arrays which are of 4 rows and two columns then it just store recent single value which i entered for last array. I used numpy for taking input for array. I tried this code:

import numpy as np
from math import *

def main ():
    i_p = input("\n Enter number of input patterns:")
    out = raw_input("\n Enter number of output nodes:")
    hidden = raw_input("\n Enter number of hidden layers:")
    print 'Patterns:'
    for p in range(0,i_p):
        print "z[%d]"%p

        rows=input("Enter no of rows:")
        cols=input("Enter no of coloumns:")
        ff=open('array.txt','w')
        for r in range(0,rows):
            for c in range(0,cols):
                z=np.matrix(input())
                ff.write(z)
                np.savetxt('array.txt',z)



if __name__=="__main__":
    main()

You are opening your file (with the same file name) inside a for loop. Every time the loop runs, the file will be overwritten with new content. — kliron
– kliron, Commented Dec 31, 2015 at 7:35

hpaulj · Accepted Answer · 2015-12-31 07:37:51Z

2

Your

np.savetxt('array.txt',z)

opens the file for a fresh write; thus it destroys anything written to that file before.

Try:

ff=open('array.txt','w')
for i in range(3):
    z = np.ones((3,5))*i
    np.savetxt(ff,z)

This should write 9 lines, with 5 columns

I was going to adapt your:

  for r in range(0,rows):
      for c in range(0,cols):
          z=np.matrix(input())
          np.savetxt...

But that doesn't make sense. You don't write by 'column' with savetxt.

Go to a Python interpreter, make a simple array (not np.matrix), and save it. Make several arrays and save those. Look at what you saved.

answered Dec 31, 2015 at 7:37

hpaulj

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3 Comments

KSuchi Over a year ago

instead of using z = np.ones((3,5))*i can i use z=np.matrix(input()) bcoz i want to take generalize input from the user.

KSuchi Over a year ago

i m trying to implement sample example for back-propagation algorithm from artificial neural network using python.so i tried above code for taking inputs for the neurons.i want to make it generalize code

hpaulj Over a year ago

np.matrix(input()) may work because matrix accepts a MATLAB like string expression. But it is not normally used in numpy. And since you are quite new to numpy I would not recommend going that route.

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