Question

I’m making a minimal case here, how should I dump the values of arrays inside array?

Multiple arrays, which contains a string value and a number, now I sort the array by second value, and read the value of the first field in order.

my @a = { "A" , 123 };
my @b = { "B" , 9 };

my @entries = ();
push @entries , \@a;
push @entries , \@b;

@entries = sort { $a[1] cmp $b[1] } @entries;
for (@entries)
{
        print @_[0] , "\n"; // should be "A\nB" after for loop
}

And what document should I view? Hmm… it’s not like normal array in array, e.g syntax like $a[0][0].

Answer 1

The first problem is that you don’t have an array of arrays there, you end up having an array of arrays of hashes because of the {} you use to construct @a and @b.
_{(BTW, a and b are poor choices as identifiers, especially given the use of scalar $a and $b in sort blocks – you don’t want to confuse yourself with what you’re dereferencing inside those sort blocks.)}

If you fix that with:

my @a = ("A", 123);
my @b = ("B", 9);

Then you fix your sort to sort numerically (cmp is a string sort, $a and $b are array references):

sort { $a->[1] <=> $b->[1] } @entries;

And then change your print line to:

print $_->[0], "\n";

you should see the result you expect.

Add use strict; use warnings; at the top of your script, and make liberal use of the Data::Dumper module to debug it.