You specifically said R, but didn't show an attempt at achieving the desired output, or mention that it was part of a larger R script. If this is an assignment, please make an attempt to solve it. So, here's a Python solution (assuming no headers, and that all values are space delimited):

Save as split_mat.py

#!/usr/bin/env python
import sys

with open(sys.argv[1], 'r') as f:
        for line in f:
                print ' '.join(''.join(i for i in line.strip().split(' ')))

Input:

00 00
11 22

Output:

0 0 0 0
1 1 2 2

Run:

python split_mat.py input.txt > output.txt