Often I have wanted to be able to sort on some sort of computed or complex value. I know map is useful to do this sort of thing. How would I for instance sort an array by the product of the second and third columns. The columns for each entry in the array are space delimited. I also want to compute the value I am sorting only once per entry in my array.
For example:

$array[0]="25 3 7";  #computed value 3*7=21
$array[1]="68 4 6";  #computed value 4*6=24;
$array[2]="23 2 3";  #computed value 2*3=6;
magic_sort(@array);  #our to be determined sort function;
#after our sort
#$array[0] is "23 2 3";  
#$array[1] is "25 3 7";
#$array[2] is "68 4 6";
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Any help or explanation as to how to do this would be much appreciated.