in reply to Problem with a sort result

Hello kzwiz,

Personally I've never seen `-` used as the comparison operator in a custom sort. This doesn't mean anything other than I've never seen it, but I do find the standard numerical comparison operator (`<=>`) provides your expected results: 

$ perl -E'
$h={foo=>{bar=>13908480193},baz=>{bar=>771918754},qux=>{bar=>288170793
+399}};
say "$_: $h->{$_}->{bar}" for sort { $h->{$b}->{bar} - $h->{$a}->{bar}
+ } keys %$h;
'
foo: 13908480193
baz: 771918754
qux: 288170793399

[download]
$ perl -E'
$h={foo=>{bar=>13908480193},baz=>{bar=>771918754},qux=>{bar=>288170793
+399}};
say "$_: $h->{$_}->{bar}" for sort { $h->{$b}->{bar} <=> $h->{$a}->{ba
+r} } keys %$h;
'
qux: 288170793399
foo: 13908480193
baz: 771918754

[download]
Hope this helps!


The way forward always starts with a minimal test.

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Re^2: Problem with a sort result
by Discipulus (Canon) on Jan 14, 2016 at 17:57 UTC
    in fact, Perl does what we tell to do, and is difficult to spot some valid Perl code that was not what we intended,but it still compile.
    The tricky part is that, contrarly to what i remembered, the sort sub must not returns -1 or 0 or +1, but:returns an integer less than, equal to, or greater than 0 so all the subtractions of octets are valid return value when choosing if $a or $b must be returned.

    L*
    There are no rules, there are no thumbs..
    Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.
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      The danger is there might be some kind of magic at work with $a, $b and the comparison operators that gets disrupted when going off book. In the case of the each function that is certainly the case.

      One world, one people

[reply]
        Looks to me like it's an integer/bigint problem: 9 digits: 
        perl -E'
$h={foo=>{bar=>10000000000},baz=>{bar=>70000000},qux=>{bar=>2000000000
+0}};
say "$_: $h->{$_}->{bar}" for sort { eval { say $h->{$b}->{bar}. " - "
+.$h->{$a}->{bar}." = ".($h->{$b}->{bar} - $h->{$a}->{bar}); $h->{$b}-
+>{bar} - $h->{$a}->{bar} } } keys %$h;
'
10000000000 - 70000000 = 9930000000
20000000000 - 10000000000 = 10000000000
qux: 20000000000
foo: 10000000000
baz: 70000000

        [download]
        the expected output is correct. 12 digits: 
        perl -E'
$h={foo=>{bar=>10000000000000},baz=>{bar=>70000000},qux=>{bar=>2000000
+0000000}};
say "$_: $h->{$_}->{bar}" for sort { eval { say $h->{$b}->{bar}. " - "
+.$h->{$a}->{bar}." = ".($h->{$b}->{bar} - $h->{$a}->{bar}); $h->{$b}-
+>{bar} - $h->{$a}->{bar} } } keys %$h;
'
20000000000000 - 70000000 = 19999930000000
10000000000000 - 70000000 = 9999930000000
foo: 10000000000000
baz: 70000000
qux: 20000000000000

        [download]
        incorrect ordering.

        rdfield

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