Concatenate Matrix PYTHON (No numpy)

Question

I am to manually merge two given matrices contained in a text file without importing any kind of module. It looks like:

[[1,2][3,4]],[[5,6,7],[8,9,10]]

I have this code:

def combine(filename): 
    with open(filename, 'r') as myfile:
        data=myfile.read().split()
        a=data[0].split()
        b=data[1].split()
    a=eval(a[0])
    b=eval(b[0])
    row_a=len(a)
    row_b=len(b)
    col_a=len(a[0])
    col_b=len(b[0])
    concatenated=[]
    if row_a==row_b: #build horizontally 
        for i in range (row_a):
            concatenated.append(a[i])
            for i in range (row_b):
                concatenated.append(b[i])
        return concatenated
    if col_a==col_b: #build vertically
        for i in range (col_a):
            concatenated.append(a[i])
            for i in range (col_b):
                concatenated.append(b[i])
        return concatenated
    else:
        print ("Error")

But it returns:

[[1, 2], [5, 6, 7], [8, 9, 10], [3, 4], [5, 6, 7], [8, 9, 10]]

Instead of:

[[1,2,5,6,7],[3,4,8,9,10]]

Any ideas on how I can make this work? Thank you in advance!

Ajax1234 · Accepted Answer · 2017-11-29 11:27:36Z

2

You can use ast.literal_eval:

import ast
final_results = [a+b for a, b in zip(*ast.literal_eval(open('filename.txt')))]

Output:

[[1, 2, 5, 6, 7], [3, 4, 8, 9, 10]]

Edit: without any imports, you can use eval. Note however that eval is quite insecure and thus must only run on strings from a trusted source:

final_results = [a+b for a, b in zip(*eval(open('filename.txt').read()))]

edited Nov 29, 2017 at 11:27

answered Nov 28, 2017 at 15:49

Ajax1234

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5 Comments

Fat Cat Over a year ago

Is there a way to do this without using import? :) Thank you!

Fat Cat Over a year ago

Thank you, if I were to just edit my existing code, is it not possible to just put concatenated=[a+b] under the if statements?

Ajax1234 Over a year ago

@FatCat please post the contents of concatenated just under the if statements.

Fat Cat Over a year ago

Would you know why I get a TypeError: eval() arg 1 must be a string, bytes or code object when I try doing this?

Ajax1234 Over a year ago

@FatCat please see my recent edit. It should work now.

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