You can swap memory for time to do this in O(1). Populate an array with your values in the distribution you want, and select a random index.

Your example, ( 1, 1.25, 3.6, 2), is ( 20/20, 25/20, 72/20, 40/20), so: 

{
    my @dist = (
                 (0) x 20,
                 (1) x 25,
                 (2) x 72,
                 (3) x 40
               );
    sub choose_weighted {
        $dist[ rand(@dist)];
    }
}

[download]
If time is not an issue, your method is fine, except that < is probably better than <= in the comparisons. That is because rand() returns a number less than one.

After Compline,
Zaxo

In reply to Re: Weighted random numbers generator by Zaxo
in thread Weighted random numbers generator by spurperl

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