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From: merlyn@iwarp.intel.com (Randal Schwartz)
Newsgroups: comp.lang.perl
Subject: Re: Needed: a pointer for a perl compare script
Message-ID: <1990Nov30.194813.17716@iwarp.intel.com>
Date: 30 Nov 90 19:48:13 GMT
References: <12020@milton.u.washington.edu>
Sender: news@iwarp.intel.com
Reply-To: merlyn@iwarp.intel.com (Randal Schwartz)
Organization: Stonehenge; netaccess via Intel, Beaverton, Oregon, USA
Lines: 58
In-Reply-To: djo7613@hardy.u.washington.edu (Dick O'Connor)

In article <12020@milton.u.washington.edu>, djo7613@hardy (Dick O'Connor) writes:
| My program reads two files of differing format which are sorted by a unique
| 5-character label.  When two labels match, a new record is written, with
| info from file A (moved around a bit) written to the "left" and info from
| file B (again, reformatted a little) written to the "right".  Where a 
| given record from file A or B has no counterpart, the same new record is
| written, with blanks on the "side" without counterpart information.
| 
| I know this is simple; it's a short program now.  But there's something
| I'm just not seeing that blocks my conversion to perl.  A pointer to a  
| suggested construct would be wonderful...I'm happy to work out the details.


Hmm... (warning... untested code follows)...

If I could fit all of file A and B into memory (my preferred tactic), I'd
do something like this:

open(A,"Afile");
while(<A>) {
	chop;
	($label,$rest) = unpack("a5a*",$_);
	$a{$label} = $rest;
	$both{$label}++;
}
close(A);
open(B,"Bfile");
while(<B>) {
	chop;
	($label,$rest) = unpack("a5a*",$_);
	$b{$label} = $rest;
	$both{$label}++;
}
close(B);
for (sort keys both) {
	$left = defined($a{$_}) ? $a{$_} : "left default";
	$right = defined($b{$_}) ? $b{$_} : "right default";
	print "$_ $left $right\n";
}

This'd probably take some massaging, but I hope you get the general
idea.  If they don't both fit into memory, you will have to do some
juggling to read from a or b depending on which of the current labels
are lower.  This solution here is much simpler (and elegant :-) by
comparison.

| BTW I've been away for two weeks; did I miss The Announcement about The Book?

The only announcement you may have missed is that Larry and I are
working intensely to incorporate the review comments and finish up the
final draft so that we can still make the Usenix deadline.

print "Just another Perl [book] hacker,"
-- 
/=Randal L. Schwartz, Stonehenge Consulting Services (503)777-0095 ==========\
| on contract to Intel's iWarp project, Beaverton, Oregon, USA, Sol III      |
| merlyn@iwarp.intel.com ...!any-MX-mailer-like-uunet!iwarp.intel.com!merlyn |
\=Cute Quote: "Intel: putting the 'backward' in 'backward compatible'..."====/