How should you read a 2D integer array?

Question

I’m new to python. I would like to read a 2D integer array from a text file, one row per line in the file, the numbers separated by commas. This works:

s = f.read()
ss = s.splitlines()
mx = []
for i in range(0,len(ss)):
    mx.append([])
    for s1 in ss[i].split(','):
        mx[i].append(int(s1))

Is there a simpler way to do this?

Asked By: xpda

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Source

Answer 1

Use a nested list comprehension:

with open(filename) as f:
    mx = [[int(x) for x in line.split(',')] for line in f]

or list comprehension with map:

mx = [map(int, line.split(',')) for line in f]

Note that in Python 3 you’ll need an extra list() call around map.

If NumPy is available:

>>> import numpy as np
>>> mx = np.loadtxt(filename, delimiter=',', dtype=int).tolist()

Answered By: Ashwini Chaudhary

Answer 2

There is a built-in module for reading comma-separated files (csv):

import csv
mx = [map(int, row) for row in csv.reader(open(filename))]

Also, if you are planning to do math with this array, you might find it useful to install and use numpy:

import numpy
mx = numpy.loadtxt(filename, delimiter=',', dtype=int)

mx will now be an array rather than a list of lists.

Answered By: chthonicdaemon

How should you read a 2D integer array?

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