Lets suppose you maintain a separate file (via make, maybe) which holds the line count for your data file. Call it data.count. 

use Tie::File;
my $count = do '/path/to/data.count';
tie my @lines, 'Tie::File', '/path/to/data.dat';
print $lines[rand $count];

[download]
Tie::File is remarkably efficient at that sort of thing. You could avoid the auxilliary count file by calling rand @lines in the array index.

I don't see any bias for or against the fencepost lines in your proposal. There is a strong bias which favors long lines and punixhes short ones.

Utf-8 is the same as ascii in the ascii range. This code will work fine with either ascii or utf-8. You may want to open your data file first and tie to the open handle. That will let you set up the '<:utf8' mode in PerlIO.

Don't pay any attention to advice to call srand in those links. That is long superceded in perl.

After Compline,
Zaxo

In reply to Re: Approach to efficiently choose a random line from a large file by Zaxo
in thread Approach to efficiently choose a random line from a large file by Your Mother

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