parse a tab delimited data using perl - perl

Question

I have a tab delimited data. I want to process that data using perl. I am a newbie to perl and could not figure out how to solve .
This is sample table: My original file is almost a GB
gi|306963568|gb|GL429799.1|_1316857_1453052 13 1
gi|306963568|gb|GL429799.1|_1316857_1453052 14 1
gi|306963568|gb|GL429799.1|_1316857_1453052 15 1
gi|306963568|gb|GL429799.1|_1316857_1453052 16 1
gi|306963568|gb|GL429799.1|_1316857_1453052 17 1
gi|306963568|gb|GL429799.1|_1316857_1453052 360 1
gi|306963568|gb|GL429799.1|_1316857_1453052 361 1
gi|306963568|gb|GL429799.1|_1316857_1453052 362 1
gi|306963568|gb|GL429799.1|_1316857_1453052 363 1
gi|306963568|gb|GL429799.1|_1316857_1453052 364 1
gi|306963568|gb|GL429799.1|_1316857_1453052 365 1
gi|306963568|gb|GL429799.1|_1316857_1453052 366 1
gi|306963580|gb|GL429787.1|_4276355_4500645 38640 1
gi|306963580|gb|GL429787.1|_4276355_4500645 38641 1
gi|306963580|gb|GL429787.1|_4276355_4500645 38642 1
gi|306963580|gb|GL429787.1|_4276355_4500645 38643 1
gi|306963580|gb|GL429787.1|_4276355_4500645 38644 1
gi|306963580|gb|GL429787.1|_4276355_4500645 38645 1
I would like to get the output as
Name, start value, end value, average
gi|306963568|gb|GL429799.1|_1316857_1453052 13 17 1
gi|306963568|gb|GL429799.1|_1316857_1453052 360 366 1
gi|306963580|gb|GL429787.1|_4276355_4500645 38640 38645 1
it will be great if someone could share their wisdom.

Answer 1

The general pattern is
use strict;
use warnings;
open my $fh, '<', 'myfile' or die $!;
while (<$fh>) {
chomp;
my #fields = split /\t/;
...
}
Within the loop the fields can be accessed as $fields[0] through $fields[2].
Update
I have understood your question better, and I think this solution will work for you. Note that it assumes the input data is sorted, as you have shown in your question.
It accumulates the start and end values, the total and the count in hash %data, and keeps a list of all the names encountered in #names so that the data can be displayed in the order it was read.
The program expects the input file name as a parameter on the command line.
You need to consider the formatting of the average because it is a floating point value. As it stands it will display the value to sixteen significant figures, and you may want to curtail that using sprintf.
use strict;
use warnings;
my ($filename) = #ARGV;
open my $fh, '<', $filename or die qq{Unable to open "$filename": $!};
my #names;
my %data;
my $current_name = '';
my $last_index;
while (<$fh>) {
chomp;
my ($name, $index, $value) = split /\t/;
if ( $current_name ne $name or $index > $last_index + 1 ) {
push #names, $name unless $data{$name};
push #{ $data{$name} }, {
start => $index,
count => 0,
total => 0,
};
$current_name = $name;
}
my $entry = $data{$name}[-1];
$entry->{end} = $index;
$entry->{count} += 1;
$entry->{total} += $value;
$last_index = $index;
}
for my $name (#names) {
for my $entry (#{ $data{$name} }) {
my ($start, $end, $total, $count) = #{$entry}{qw/ start end total count /};
print join("\t", $name, $start, $end, $total / $count), "\n";
}
}
output
gi|306963568|gb|GL429799.1|_1316857_1453052 13 17 1
gi|306963568|gb|GL429799.1|_1316857_1453052 360 366 1
gi|306963580|gb|GL429787.1|_4276355_4500645 38640 38645 1

Answer 2

This will produce the same output for the sample in your question:
#!/usr/bin/env perl -n
#
my ($name, $i, $value) = split(/\t/);
sub print_stats {
print join("\t", $prev_name, $start, $prev_i, $sum / ($prev_i - $start + 1)), "\n";
}
if ($prev_name eq $name && $i == $prev_i + 1) {
$sum += $value;
$prev_i = $i;
}
else {
if ($prev_name) {
&print_stats();
}
$start = $i;
$prev_name = $name;
$sum = $value;
$prev_i = $i;
}
END {
&print_stats();
}
Use it as:
./parser.pl < sample.txt
UPDATE: answers to the questions in comments:
To print output to a file, run like this: ./parser.pl < sample.txt > output.txt
$prev_name and $prev_i are NOT initialized, so they are undef at first (= NULL)

Answer 3

You could do something like this....
open (FILE, 'data.txt');
while (<FILE>) {
chomp;
($name, $start_value, $end_value, $average) = split("\t");
print "Name: $name\n";
print "Start Value: $start_value\n";
print "End Value: $End_Value\n";
print "Average: %average
print "---------\n";
}
close (FILE);
exit;
Those look like GenBank files...so I'm unsure where you are getting the start, end values, average.

Answer 4

Here's an example using Text::CSV:
use Text::CSV; # This will implicitly use Text::CSV_XS if it's installed
my $parser = Text::CSV->new( { sep_char => '|' } );
open my $fh, '<', 'myfile' or die $!;
while (my $row = $parser->getline($fh)) {
# $row references an array of field values from the line just read
}
Also, as a minor side detail, your sample data is delimited by pipe characters, not tabs, although that may just be to avoid copy/paste errors for those answering your question. If the actual data is tab-delimited, set sep_char to "\t" instead of '|'.