I guess we have different understandings of the term In-place sort.

Yes, inside perl internals, "inplace" just means that instead of passing the elements on the stack, a reference to the target array is passed and the sorting is done directly over it.

... but if the quicksort algorithm is selected, @a = sort @a is also an in-place sort as described on the article pointed by you (if we ignore degenerated cases).

If you need 1.4GB to sort 400MB, it means that you are probably converting numbers to strings inside the sort. For instance: 

use Memchmark 'cmpthese';

use sort '_quicksort';

cmpthese( none => sub {
             my @a = map { int rand 100 } 1..1000000;
          },
          sort_num => sub {
             my @a = map { int rand 100 } 1..1000000;
             @a = sort { $a<=> $b } @a
          },
          sort_str => sub {
             my @a = map { int rand 100 } 1..1000000;
             @a = sort { $a cmp $b } @a
          },
          sort_str_workaround => sub {
             my @a = map { int rand 100 } 1..1000000;
             my ($c, $d);
             @a = sort { ($c, $d) = ($a,$b); $c cmp $d } @a
          }
        );

__END__

test: none,                memory used:  3997696 bytes
test: sort_num,            memory used:  3997696 bytes
test: sort_str,            memory used: 68202496 bytes
test: sort_str_workaround, memory used:  3997696 bytes

[download]
... and as you can see, there is a simple workaround (though it would make the sorting much slower).

In reply to Re^5: Howto Avoid Memory Problem in List::MoreUtils by salva
in thread Howto Avoid Memory Problem in List::MoreUtils by Anonymous Monk

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