in reply to Sorting a hash of arrays based on a particular array element.

Supply the keys of %hash to sort and then use $hash{ $a | $b }[0] to access your sort field: 

%hash = ( 1 => [ 51, 'a2'], 2 => [42, 'a1'] );;
# NOTE: ^______ parens not curlies _________^

print "$_ => @{$hash{$_}}" 
    for sort{ $hash{$a}[0] <=> $hash{$b}[0] } keys %hash;;

2 => 42 a1
1 => 51 a2

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Realise that you will need sort the hash each time you want to iterate it in sorted order (or use one of the sorted hash implementations on CPAN ).

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