FAQ 5.39 How do I select a random line from a file?
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From: PerlFAQ Server on 19 May 2010 12:00 This is an excerpt from the latest version perlfaq5.pod, which comes with the standard Perl distribution. These postings aim to reduce the number of repeated questions as well as allow the community to review and update the answers. The latest version of the complete perlfaq is at http://faq.perl.org . -------------------------------------------------------------------- 5.39: How do I select a random line from a file? Short of loading the file into a database or pre-indexing the lines in the file, there are a couple of things that you can do. Here's a reservoir-sampling algorithm from the Camel Book: srand; rand($.) < 1 && ($line = $_) while <>; This has a significant advantage in space over reading the whole file in. You can find a proof of this method in *The Art of Computer Programming*, Volume 2, Section 3.4.2, by Donald E. Knuth. You can use the "File::Random" module which provides a function for that algorithm: use File::Random qw/random_line/; my $line = random_line($filename); Another way is to use the "Tie::File" module, which treats the entire file as an array. Simply access a random array element. -------------------------------------------------------------------- The perlfaq-workers, a group of volunteers, maintain the perlfaq. They are not necessarily experts in every domain where Perl might show up, so please include as much information as possible and relevant in any corrections. The perlfaq-workers also don't have access to every operating system or platform, so please include relevant details for corrections to examples that do not work on particular platforms. Working code is greatly appreciated. If you'd like to help maintain the perlfaq, see the details in perlfaq.pod. |