How to write an array to a file in python?

[k voller]

Hi, I have generated an array of random numbers and I'm trying to then write this array to a .txt file but the code I have written doesn't seem to do this correctly. I'm fairly new to python so any help on this would be great. Here is what I have so far:

import numpy as N
import random

def main():
   n=10
   size=1500
   initial=N.zeros([n,3], dtype=N.float64)
   filename="positions.txt"

   for i in range(n):
      for j in range(0,3):
         initial[i,j]=random.randrange(0,size)
   file=open(filename,'w')
   file.write(initial)
   file.close()

[bvdet]

You have to convert the array into a string before attempting to write it to a file. What should the file look like?

[bvdet]

You can also write the array to disk using array method tofile. The shape, type or endianness are not stored in the file.

[bvdet]

I would probably do it as shown below where arr is the array you created in your post:

f = open("numpytest.txt", "w")
f.write("\n".join([",".join([str(n) for n in item]) for item in arr.tolist()]))
f.close()

The shape of the array is preserved, and you could recreate the array from the file.

[k voller]

thanks that has worked well but I'm struggling to recreate the array from the .txt file. How can I now access the numbers in the file and put them into an array if they are not already part of a list or array?

[bvdet]

Read the file, parse into a list of lists, type cast to float, initialize new array, iterate on data and add each number to array.

dataList = [[float(s) for s in item.strip().split(",")] for item in open("numpytest.txt").readlines()]
rows = len(dataList)
cols = len(dataList[0])
arr1 = N.zeros([rows,cols], dtype=N.float64)
for i, row in enumerate(dataList):
    for j, number in enumerate(row):
        arr1[i][j] = number