Path: utzoo!attcan!uunet!samsung!think!mintaka!ogicse!schaefer
From: schaefer@ogicse.ogi.edu (Barton E. Schaefer)
Newsgroups: comp.lang.perl
Subject: Ordering one array by another
Message-ID: <8251@ogicse.ogi.edu>
Date: 27 Mar 90 01:28:29 GMT
Organization: Oregon Graduate Institute (formerly OGC), Beaverton, OR
Lines: 41

I have a sorted list of keywords, and a file (well, stdin actually, but
no matter) consisting of lines each of which contains at most one of the
keywords.  There may be keywords not in the file, and lines with zero
keywords (which are ignored), but no pair of lines both contain the same
keyword.  What I want to do is reorder the input lines to match the order
in the list of keywords.

So what's the fastest way?  What I have right now goes like this:

    @lines = <STDIN>;				# Whomp it in
    # Never mind how I got the sorted keywords, they're in @keys
    foreach $k (@keys) {			# For every keyword
	$i = $[;				# Reset the index
	foreach $l (@lines) {			# For every line
	    if ($l =~ /\b$k\b/) {		# If it matches
		print splice(@lines,$i,1);	# Remove and print it
		last;				# Done with this pass
	    }
	    $i++;				# Increment index
	}
    }

The idea being that the splice shortens the search for each succeeding
pass through the lines.

Of course Randal would point out that it could be:

    grep(($k = $_, $i = 0, $found = 0,
	grep((!$found && ++$i && /\b$k\b/ &&
		(print(splice(@lines,$i-1,1)), ++$found)),
	    @lines)),
	@keys);

I'm wondering if there isn't some trick to do this faster than either of
these, perhaps by mixing grep and foreach, or using an associative array.
Suggestions?
-- 
Bart Schaefer          "EARTH: Surrender IMMEDIATELY or we PICKLE DAN QUAYLE"

                                                                    "THPPFT!"
schaefer@cse.ogi.edu (used to be cse.ogc.edu)