Hi BrowserUk,

I'm still running into trouble. Here is my code:

#!/usr/bin/perl -w
use strict;
use Data::Dump qw[ pp ];

open my $fh, '<', 'numbs.dat' or die $!;

my $pick = genPicker( $fh ); ## Reads the file and generates a picker

sub genPicker {
    my $fh = shift;
    my( @vals, @odds ); ( $vals[ @vals ], $odds[ @odds ] ) = split( ' 
+' ) for <$fh>;

    ## Sort if not sorted
    my @order = sort{ $odds[ $a ] <=> $odds[ $b ] } 0 .. $#odds;
    @odds = @odds[ @order ];
    @vals = @vals[ @order ];

    ## Calculate and accumulate break points
    my $t = 0; $t += $_ for @odds;
    $_ /= $t for @odds;
    $odds[ $_ + 1 ] += $odds[ $_ ] for 0 .. $#odds - 1;

    ## Generate a subroutine to do the picking
    return sub {
        my $r = rand();
        $r < $odds[ $_ ] and return $vals[ $_ ] for 0 .. $#odds;
    };
}

close $fh;
[download]

Here is my numbs.dat file (I changed the numbers to simplify things):

A 0.0001
B 0.0004
C 0.0008
[download]

For what it's worth, there is a new line after each row except the last, and each letter is separated from the corresponding number by a single space. I think something is going wrong with my split, because if I pause the script and look into the variables, my @odds array has three slots, each of which is undefined, whereas my @vals array has three slots, each of which contains a letter, a space, a number and then for the first two slots a new line character.

Do you see what's wrong?

Best wishes,

Eric

Do you see what's wrong?

Maybe. When you C&P'd the code, you did so without using [download] link first.

Because of that, one of the longer lines has been (moronically and pointlessly) "wrapped" by the PM website, and extra characters insertewd. Hence the line that should be:

    my( @vals, @odds ); ( $vals[ @vals ], $odds[ @odds ] ) = split( ' 
+' ) for <$fh>;
[download]

Has been autofcuked into:

    my( @vals, @odds ); ( $vals[ @vals ], $odds[ @odds ] ) = split( ' 
+' ) for <$fh>;
[download]

Change that back and see how you get on. (Did you really get no warnings or errors?)

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Hi BrowserUk,

That was it. Thanks so much!!!

Sorry - I didn't mean to imply that there weren't warnings and errors - there were. They led me to look into what was in @odds and @vals.

Your code is eye opening for me. I still haven't figured all of it out, but it's way more concise than I write things. You write stuff in one simple line that it would take me several more convoluted lines. I've got a lot to learn and may be back with more questions.

Best wishes, Eric

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