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Postings from April 2012
At 10:21 AM -0230 4/9/12, Tiago Hori wrote:
>Sorry guys,
>
>Another quick question:
>
>I got this from perlmonks:
>
>#!/usr/bin/perl -w use strict; my @desired_cols = qw(colname1 colname3);
>#order matters here # reads first line to get actual column names my
>$header_line = (<DATA>); my @actual_cols = split(/\s+/,$header_line); # get
>column number of the actual column names my $pos =0; my %col2_num = map {$_
>=> $pos++}@actual_cols; # translate the desired col names into position
>numbers my @slice = map{$col2_num{$_}}@desired_cols; print
>join("\t",@desired_cols),"\n"; #header line while (<DATA>) { my @row =
>(split)[@slice]; print join("\t",@row),"\n"; #each data row }
>
>
>It is working great fro me and I understand almost all of it. The only
>thing I don't get is why you have to split the @slice array into the new
>@row array inside the while loop instead of using the @slice array. Doesn't
>using split on a array creates a list, which is then assigned to an array
>and in effect creates a copy of the original array?
The line
my @row =(split)[@slice];
does not split the @slice array because split is enclosed in
parentheses. 'split' by itself with no arguments will split the $_
variable on whitespace. This results in a list, which is then indexed
by @slice, an array of integers. That results in a slice of the list
returned by split, consisting of the desired columns in the line,
which are the stored in the @row array.
.
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