Perl：增加2D数组单元格？

Question

I have a set of numerical data for which is important to me to know what pairs of numbers occurred together, and how many times. Each set of data contain 7 numbers betwen 1 and 20. There are several hundred sets of data.

Essentially, by parsing each set of my data, I want to create a 20 x 20 array that I can use to keep a count of when pairs of numbers occurred together.

I have done a lot of searching, but maybe I've used the wrong key words. I've seen loads of examples how to create a "2D array" - I know perl doesn't actually do that, and that it's really an array of references - and to print the values contained therein, but nothing really on how to work with one particular cell by number and alter it.

Below is my conceptual code. The commented lines don't work, but illustrate what I want to achieve. I'm reasonably new to coding perl, and this just seems to advanced for me to understand the examples I've seen and translate it into something I can actually use.

my @datapairs;
while (<DATAFILE>)
{
  chomp;
  my @data = split(",",$_);
  for ($prcount=0; $prcount <=5; $prcount++) 
  {
    for ($othcount=($prcount+1); $othcount<=6; $othcount++)
    {
        @data[$prcount]=@data[$prcount]+1;
        @data[$othcount]=@data[$othcount]+1;
        @data[$prcount]=@data[$prcount]-1;
        @data[$othcount]=@data[$othcount]-1;
        print @data[$prcount]." ".@data[$othcount]."; ";
        #@datapairs[@data[$prcount]][@data[$othcount]]++;
        #@datapairs[@data[$othcount]][@data[$prcount]]++;
    }
  }
}

Any input or suggestions would be much appreciated.

Answer 1

To access a "cell" in a "2-d array" in Perl (as you alredy figured out, it's an array of arrayrefs), is simple:

my @datapairs;
# Add 1 for a pair with indexes $i and $j 
$datapairs[$i]->[$j]++;
print that value
print "$datapairs[$i]->[$j]\n";

It's not clear what you mean by "occur together" - if you mean "in the same length-7 array", it's easy:

my @datapairs;
while (<DATAFILE>) {
    chomp;
    my @data = split(",", $_);
    for (my $prcount = 0; $prcount <= 5; $prcount++) {
        for (my $othcount = $prcount + 1; $othcount <=6 ; $othcount++) {
            $datapairs[ $data[$prcount] ]->[ $data[$othcount] ]++;
        }
    }
}
# Print
for (my $i = 0; $i < 20; $i++) {
    for (my $j = 0; $j < 20; $j++) {
        print "$datapairs[$i]->[$j], ";
    }
    print "\n";
}

---

As a side note, personally, just for stylistic reasons, I strongly prefer to reference EVERYTHING, eg use arrayref of arrayrefs instead of array of arrays. Eg

my $datapairs;
# Add 1 for a pair with indexes $i and $j 
$datapairs->[$i]->[$j]++;
print that value
print "$datapairs->[$i]->[$j]\n";

The second (and third...) arrow dereference operator is optional in Perl but I personally find it significantly more readable to enforce its usage - it spaces out the index expressions.