Randomizing All Lines
Problem
You want to copy a file and randomly reorder its lines.
Solution
Read all lines into an array, shuffle the array using the algorithm from Section 4.17, and write the shuffled lines back out:
# assumes the &shuffle sub from Chapter 4 while (<INPUT>) { push(@lines, $_); } fisher_yates_shuffle(\@lines); foreach (@reordered) { print OUTPUT $_; }
Discussion
The easiest approach is to read all lines into memory and shuffle
them there. Because you don’t know where lines start in the
file, you can’t just shuffle a list of line numbers and then
extract the lines in the order they’ll appear in the shuffled
file. Even if you did know their starts, it
would probably still be slower because you’d be
seek
ing around in the file instead of simply
reading it from start to finish.
See Also
Get Perl Cookbook now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.