Matrix input from a text file(python 3)

Question

Im trying to find a way to be able to input a matrix from a text file;

for example, a text file would contain

1 2 3
4 5 6
7 8 9

And it would make a matrix with those numbers and put it in matrix = [[1,2,3],[4,5,6],[7,8,9]]

And then this has to be compatible with the way I print the matrix:

 print('\n'.join([' '.join(map(str, row)) for row in matrix]))

So far,I tried this

chemin = input('entrez le chemin du fichier')

        path = input('enter file location') 

        f = open ( path , 'r')
        matrix = [ map(int,line.split(','))) for line in f if line.strip() != "" ]

All it does is return me a map object and return an error when I try to print the matrix.

What am I doing wrong? Matrix should contain the matrix read from the text file and not map object,and I dont want to use external library such as numpy

Thanks

A.J. Uppal · Accepted Answer · 2014-05-06 00:50:02Z

2

You can use list comprehension as such:

myfile.txt:

1 2 3
4 5 6
7 8 9


>>> matrix = open('myfile.txt').read()
>>> matrix = [item.split() for item in matrix.split('\n')[:-1]]
>>> matrix
[['1', '2', '3'], ['4', '5', '6'], ['7', '8', '9']]
>>>

You can also create a function for this:

>>> def matrix(file):
...     contents = open(file).read()
...     return [item.split() for item in contents.split('\n')[:-1]]
... 
>>> matrix('myfile.txt')
[['1', '2', '3'], ['4', '5', '6'], ['7', '8', '9']]
>>>

answered May 6, 2014 at 0:50

A.J. Uppal

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2 Comments

Program_coder Over a year ago

Thanks for helping; I tried your list comprehension,however,I created a file with the matrix 1 2 3,under those,4 5 6 and under 4 5 6, 7 8 9; It doest work but only write 1 2 3 and 4 5 6 in the matrix, 7 8 9 is not showing/saved?

Program_coder Over a year ago

I removed [:-1] from your code and now it works as I wish; what was [:-1] for? Thanks

Andrei · Accepted Answer · 2018-03-05 21:53:08Z

0

is working with both python2(e.g. Python 2.7.10) and python3(e.g. Python 3.6.4)

rows=3
cols=3
with open('in.txt') as f:
   data = []
   for i in range(0, rows):
      data.append(list(map(int, f.readline().split()[:cols])))
print (data)

edited Mar 5, 2018 at 21:53

answered Mar 30, 2016 at 18:28

Andrei

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