Hi BrowserUk,

I have another question about your code, specifically about this piece: 

    return sub {
        my $r = rand();
        $r < $odds[ $_ ] and return $vals[ $_ ] for 0 .. $#odds;
    };

[download]

I described my problem as having a list of values - A, B, C, etc. - and relative odds corresponding to choosing those values. I have tried to incorporate your code into a script in which I pass a %vals_odds hash to your genPicker subroutine. Things seem to go well until the return statement, but then nothing is returned with this statement in the main body of my script:

my $pick = genPickerConverted(\%kmer_prob);

And if I step through the code, right before I would enter the "return" block above, my @odds array has cumulative relative odds in it (so it ends with a 1, as it should), but then it never enters the "return" block.

My understanding of the return block (which looked fairly foreign to me when I saw it) is as follows: 

# return something that is going to come from ... 
# ... an unnamed subroutine (unnamed ... 
# ... because there's nothing between "sub" and "{"
    return sub {

       # r is a random number >= 0 < 1
        my $r = rand();

       # an implicit if statement: 
       # if, when going through every value of odds from lowest ... 
       # ... to highest,  r is less than that value of odds, this ... 
       # ... code will go on to the "and" statement, and otherwise... 
       # ... it will go on to the next value in @odds
       # if it gets to the "and" statement, it will return the ... 
       # ... corresponding value for @vals to the subroutine ... 
       # ... call, which will, in turn, return that to the main ... 
       # body of the script
        $r < $odds[ $_ ] and return $vals[ $_ ] for 0 .. $#odds;

    };

[download]

Is my understanding of the "return" block correct? And why does my code not get in there when I pass my vals and odds to the subroutine as a hash rather than a file handle? (I've changed the code so that I can tell that my hash gets in there correctly and is converted to @vals and @odds as I expect.) I'd include more code except that it gets really long and, I think, just adds confusion to my question.

Thanks.

Eric

In reply to Re^8: an algorithm to randomly pick items that are present at different frequencies by efoss
in thread an algorithm to randomly pick items that are present at different frequencies by efoss

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