How do I turn a table into a matrix?

If I got a table in a text file such like

A B 1
A C 2
A D 1
B A 3
C D 2
A E 1
E D 2
C B 2
. . .
. . .
. . .

And I got another symbol list in another text file. I want to transform this table into a Perl data structure like:

_ A D E . . .
A 0 1 1 . . .
D 1 0 2 . . .
E 1 2 0 . . .
. . . . . . .

But I only need some selected symbol, for example A, D and E are selected in the symbol text but B and C are not.

Solution

Use an array for the first one and a 2-dimentional hash for the second one. The first one should look roughly like:

$list[0] # row 1 - the value is "A B 1"

And the hash like:

$hash{A}{A} # the intersection of A and A - the value is 0

Figuring out how to implement a problem is about 75% of the mental battle for me. I'm not going to go into specifics about how to print the hash or the array, because that's easy and I'm also not entirely clear on how you want it printed or how much you want printed. But converting the array to the hash should look a bit like this:

foreach (@list) {
  my ($letter1, $letter2, $value) = split(/ /);
  $hash{$letter1}{$letter2} = $value;
}

At least, I think that's what you're looking for. If you really want you could use a regular expression, but that's probably overkill for just extracting 3 values out of a string.

EDIT: Of course, you could forgo the @list and just assemble the hash straight from the file. But that's your job to figure out, not mine.