sourcecode
tfrayner
<CODE>
#! /usr/bin/perl -w
# To Do: more error checking, get --delimiter to work for \t.
# cols2lines.pl takes an input file with fields separated
# by the chosen delimiter (default is the tab stop) and
# switches the columns into rows (and vice versa,
# obviously). The script can be called with the input file,
# or both input and output files as its arguments. If one or
# both are omitted from the command line the user is prompted
# for their location. The delimiter can be defined using the
# -d or --delimiter switch. The delimiter may be double-
# quoted if necessary. In non-interactive mode the output
# file will not overwrite an existing file unless the -f or
# --force switch is used. Use the -h or --help
# switch to get a usage summary.
use strict;
use Getopt::Long;
# DECLARE GLOBALS
my $delimiter = "\t"; # default delimiter is tab stop
my $infile = "";
my $outfile = "";
# PARSE ARGUMENTS
sub parseargs{
my $force;
my $helptext;
&GetOptions("d|delimiter=s" => \$delimiter,
"f|force" => \$force,
"h|help" => \$helptext);
if ($helptext){
die ("Usage: cols2lines [-h] [-f] [-d <delimiter>]".
" [input file] [output file]\n");
}
if (@ARGV){
$infile=shift (@ARGV);
unless (-e $infile){die ("File \'$infile\' not found.\n");}
$outfile=shift (@ARGV);
if ((-e $outfile) and !$force){
die ("File \'$outfile\' aleady exists. Use -f to".
" force overwrite.\a\n");
}
} else {
$infile="";
$outfile="";
}
return ($infile, $outfile);
}
# ASSIGN INPUT FILE
sub queryinfile {
$infile="";
until (-e $infile){
print ("Please enter the name of the input file:\n");
$infile = <STDIN>;
chomp ($infile);
unless (-e $infile){
print STDERR ("File \'$infile\' not found. ".
"Ctrl-C to exit.\a\n");
}
}
$infile;
}
# ASSIGN OUTPUT FILE
sub queryoutfile {
print ("Please enter the name of the output file:\n");
$outfile = <STDIN>;
chomp ($outfile);
if (-e $outfile){
print STDERR ("File \'$outfile\' aleady exists. ".
"Overwrite? [Y\/N]\a\n");
my $answer = <STDIN>;
chomp ($answer);
if (lc($answer) ne 'y'){die ("Script aborted by user.\n");}
}
$outfile;
}
# PERFORM OPERATION
sub bigfile_colstolines {
my $infile = shift;
my $outfile = shift;
my $infilehandle = "<$infile"; # read-only
open (INFILE, $infilehandle) or die ("File error.\a\n");
my $outfilehandle = ">$outfile"; # write only
open (OUTFILE, $outfilehandle) or die ("Output failure.\a\n");
my $line = <INFILE>;
my @testarray = split (/$delimiter/, $line);
seek(INFILE,0,0);
for (my $counter=0; $counter <= $#testarray; $counter++){
my @columnarray = undef();
while (defined ($line = <INFILE>)){
chomp ($line);
my @linearray = split (/$delimiter/, $line);
push (@columnarray, $linearray [$counter]);
}
shift (@columnarray); # removes unwanted characters
my $newline = join $delimiter, (@columnarray);
print OUTFILE ($newline, "\n");
seek(INFILE,0,0);
}
close(INFILE);
close(OUTFILE);
}
# MAIN LOOP
($infile, $outfile)=&parseargs;
unless ($infile){$infile=&queryinfile;}
unless ($outfile){$outfile=&queryoutfile;}
&bigfile_colstolines ($infile, $outfile);
print ("Done.\n");
exit
</CODE>
Time once again to reinvent the wheel, I suspect. I wrote this a couple of years back as an exercise in perl. Specifically, a friend of mine was wanting to manipulate large (>10GB) tables of data. Part of his analysis involved transposing a table such that the columns became lines and vice versa. As a result I wrote this rather convoluted script. It only loads one line of the table into memory at a time, rather than the whole table.
<p>
The other points of this exercise were to make the code as well-structured (whatever that means :-P) and as user-friendly as possible. I imagine it's possible to load the essential functionality into a single line, but that wasn't my aim here.
<p>
Of course, I imagine there's a perfectly good CPAN module out there which would do this much better than this :-)
<p>
<b>Update:</b> The original script opened and closed the input file with each column that it read. I've changed to the more efficient [seek] function suggested by [RhetTbull].
Utility scripts
Tim Rayner
<br>tfrayner@yahoo.co.uk