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POHow can I get exactly n random lines from a file with Perl?
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2009-05-13T07:07:41.617
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2017-05-23T12:30:25.083
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Following up on <a href="https://stackoverflow.com/questions/448005/whats-an-easy-way-to-read-random-line-from-a-file-in-unix-command-line" title="What’s an easy way to read random line from a file in Unix command line?">this</a> question, I need to get exactly <code>n</code> lines at random out of a file (or <code>stdin</code>). This would be similar to <code>head</code> or <code>tail</code>, except I want some from the middle. Now, other than looping over the file with the solutions to the linked question, what's the best way to get exactly <code>n</code> lines in one run? For reference, I tried this: <pre><code>#!/usr/bin/perl -w use strict; my $ratio = shift; print $ratio, "\n"; while () { print if ((int rand $ratio) == 1); } </code></pre> where <code>$ratio</code> is the rough percentage of lines I want. For instance, if I want 1 in 10 lines: <pre><code>random_select 10 a.list </code></pre> However, this doesn't give me an exact amount: <pre><code>aaa> foreach i ( 0 1 2 3 4 5 6 7 8 9 ) foreach? random_select 10 a.list | wc -l foreach? end 4739 4865 4739 4889 4934 4809 4712 4842 4814 4817 </code></pre> The other thought I had was slurping the input file and then choosing <code>n</code> at random from the array, but that's a problem if I have a really big file. Any ideas? Edit: This is an exact duplicate of <a href="https://stackoverflow.com/questions/692312/randomly-pick-lines-from-a-file-without-slurping-it-with-unix" title="Randomly Pick Lines From a File Without Slurping It With Unix">this</a> question.
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<perl><random-sample><file-processing>
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How can I get exactly n random lines from a file with Perl?
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