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Re: Efficiently selecting a random, weighted element

by Skeeve (Vicar)
on Oct 16, 2006 at 13:08 UTC ( #578498=note: print w/replies, xml ) Need Help??


in reply to Efficiently selecting a random, weighted element

I'd not store the index, where the file begines, but the number of words in it.

Searching is then done by substracting the number of words from the random number.

As a final step, the file found is swapped with the last file and the number of words is substracted.

#!/usr/bin/perl use strict; use warnings; my @number_of_words = ( { number => 10, name => 'file_a.txt' }, { number => 1, name => 'file_b.txt' }, { number => 3, name => 'file_c.txt' }, { number => 5, name => 'file_d.txt' }, { number => 10, name => 'file_e.txt' }, ); my $total_number_of_words = 29; my $select= 3; my $selected= 0; while ( $select-- ) { my $randomindex= rand $total_number_of_words; my $last_index= ( scalar @number_of_words ) - $selected - 1; my $i= $last_index+1; do { $randomindex-= $number_of_words[--$i]->{'number'}; } while ( $randomindex >= 0 ); $total_number_of_words-= $number_of_words[$i]->{'number'}; # print $number_of_words[$i]->{'name'},"\n"; @number_of_words[$i, $last_index]= @number_of_words[$last_index, $ +i]; ++$selected; } for (my $i= $#number_of_words - $selected; ++$i<=$#number_of_words;) { print $number_of_words[$i]->{'name'},"\n"; }
As you can see, your selected files are now in the last n positions of the array.


s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e

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