Finding a random line

Jettra has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Finding a random line by clemburg (Curate) on Jan 17, 2001 at 14:07 UTC
You want to read the Perl Cookbook, chapter 8 (File Contents), page 284-285. For your convenience, I put the code that does what you want in here. Solution: Use `rand()` and `$.` to decide which line to keep: `rand($.) < 1 && ($line = $_) while <>; # $line is the random line` [download] This works because you have a 1/N chance for line N to be kept. For more explanations, get the book. Extending this example to choosing a random word from an array of words is left as an exercise for the reader (I always wanted to say that!) ... Christian Lemburg Brainbench MVP for Perl http://www.brainbench.com	[reply] [d/l] [select]
Re: Finding a random line by dkubb (Deacon) on Jan 17, 2001 at 12:56 UTC
Here's a link explaining the fastest way that I've found to do this here: Random Line from a file.	[reply]
Re: Finding a random line by lemming (Priest) on Jan 17, 2001 at 12:58 UTC
Before we can really answer your question: In what manner of efficiency do you want? Would placing all lines in an array and picking a random number based on the size work or too memory intensive? Would checking the size of the file with "wc -l" and then reading down a random number of lines work? Or is that not portable enough? You could read the file twice to avoid the "wc -l" which is a bit intensive, but the filesytem may give you leeway with buffering. You could massage the data so that the leading line has the # to go off of. Or even better create a file with the size data in the first block you read and then seek to the random spot. If none of this gives a clue for you to go off of, then please give more info back.	[reply]
Re: Finding a random line by I0 (Priest) on Jan 18, 2001 at 02:02 UTC
perldoc -q "How do I select a random line from a file?"	[reply]
Re: Finding a random line by EvanK (Chaplain) on Jan 17, 2001 at 23:47 UTC
Wait wait, do you want a single line or a single word? If a line, then: `srand; # seed the random generator open(FILE,"file.txt"); # put the file contents into an array @file = <FILE>; close(FILE); foreach (@file) {chomp} # remove the newlines $line = $file[rand($#file)]; # select a random line` [download] If a word: `srand; # seed the random generator open(FILE,"file.txt"); # put the file contents into one big scalar while(<FILE>) { $file .= <FILE>; } close(FILE); $file =~ s/\r/ /g; # remove carriage returns and replace them with spa +ces $file =~ s/\s+/\s/g; # remove multiple consecutive spaces @file = qw($file); # seperate the file into single words $word = $file[rand($#file)]; # select a random word` [download] The code is kind of comment-laden, but they're just so you know what's what. ______________________________________________ When I get a little money, I buy books. If I have any left over, I buy food and clothes. -Erasmus	[reply] [d/l] [select]