parsing table in perl [closed] - linux

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Suppose i have following table in table format( text format, in linux).
index score rank mark
0 100 0 4
1 873 23 89
2 500 15 90
3 224 30 115
and so on( more rows and column)..
#!/usr/bin/perl
open ($fh, '<', "data.txt")
or die "Couldn't open file file.txt, $!";
while ($line= <$fh>) {
chomp $line;
#field = split "\t",$line;
print "field\n";
}
close $fh;
what I need is, to delete some instant, and paste in another file, like
a) delete all instance of rank<= (less than equal) 15 and paste in another file
b) compare rank & mark , if difference is >10 , then delete and paste in another file.
please help..
thank you

Answer 1

Not an answer but some annotations, which do not fit into a comment.
Use strict and warnings, if you start learning Perl.
Declare variables with my.
Don't declare variables, you do not need ($line).
In Perl you can declare variables in list form.
If you do not chomp the input you can output it unmodified.
Splitting with a regular expression is more robust, than relying on a tab.
Example:
#!/usr/bin/perl
use strict;
use warnings;
while (<DATA>) {
if (/^index/) { print; next; }
my ($index, $score, $rank, $mark) = split /\s+/;
print unless int($rank) < 15;
}
__DATA__
index score rank mark
0 100 0 4
1 873 23 89
2 500 15 90
3 224 30 115
Output:
index score rank mark
1 873 23 89
2 500 15 90
3 224 30 115
The DATA change is just for a minimal reproducible example. Keep your file handling.

Answer 2

Start by adding some abstractions:
use strict;
use warnings;
use autodie; # Will crash the program if open, close, or print fails.
sub read_line {
my ($fh) = #_;
chomp(my $line = <$fh>);
return undef unless defined $line;
return split " ", $line;
}
sub write_line {
my ($fh, #fields) = #_;
say $fh join("\t", #fields);
}
Now you can open the various files for reading/writing and copy the header into output files:
open(my $input, "<", "data.txt");
open(my $default_out, ">", "data_new.txt");
open(my $low_rank, ">", "lowrank.txt");
open(my $large_diff, ">", "large_diff.txt");
my #header = read_line($input);
write_line($default_out, #header);
write_line($low_rank, #header);
write_line($large_diff, #header);
The main loop is now just a matter of reading lines (making sure to stop if read_line returns undef) and following the rules:
while (defined(my #fields = read_line($input))) {
my ($index, $score, $rank, $mark) = #fields;
if ($rank <= 15) {
write_line($low_rank, #fields);
} elsif (...) { # fill in the condition for large_diff yourself
write_line($large_diff, #fields);
} else {
write_line($default_out, #fields);
}
}