Question

How do I build a 2d matrix using STDIN?

If I input a matrix like so:

1 2 3
4 5 6
7 5 6

7 8 9
4 5 6
3 3 3

how do I input this and create two matrices out of this?

Here’s my code so far

while (defined ($a=<STDIN>)) {
    chomp ($a);
    push @a,($a);
    }   

This is just for the input.

My understanding is I can just add each row to a stack. When the matrices are all put in I can take each line, break by space to create an array. I then need to create an array reference and push this reference into an array to create my matrix. How the heck do I do this? Is there an easier way? I’ve been bashing my head on this for 3 days now. I feel pretty damn stupid right now…

Answer 1

The other answers seem to be missing the requirement to read multiple matrices from the same input, breaking on a blank line. There are a few different ways to go about this, including frobbing $/, but here’s one that appeals to me.

# Read a matrix from a handle, with columns delimited by whitespace
# and rows delimited by newlines. A matrix ends at a blank line
# (which is consumed) or EOF.
sub read_matrix_from {
  my ($handle) = @_;
  my @out;
  while (<$handle>) {
    last unless /\S/;
    push @out, [ split ];
  }
  return \@out;
}

my @matrices;
push @matrices, read_matrix_from(\*ARGV) until eof();

Season the last part to taste, of course — you might be using an explicitly opened handle instead of ARGV magic, and you might know in advance how many things you’re reading instead of going to EOF, etc.