Thanks, Jim.
This awesome!
T.
Sent from my iPhone
On 2013-02-11, at 11:49 AM, Jim Gibson <jimsgib...@gmail.com> wrote:
>
> On Feb 10, 2013, at 5:57 PM, Tiago Hori wrote:
>
>> Hi All,
>>
>> I am trying to force myself to not use one of perl's modules to parse tab
>> delimited files (like TXT::CSV), so please be patient and don't tell me
>> just to go and use them. I am trying to re-ivent the wheel, so to speak,
>> because as we do with science, we repeat experiments to lean about the
>> process even tough we know the outcome.
>
> Coding your own solutions rather than using a module already built for the
> same purpose is perfectly all right, especially if you are learning Perl. If
> you are confident your data has a simple format and will not change, then you
> can parse it yourself. Keep in mind, however, that the Text::CSV module can
> handle more complicated cases. For example, what if your data fields can
> contain the separator character? In that case, your data fields may be
> enclosed in quotes or the embedded separator characters will have to be
> escaped (e.g., preceded by a '\' character or some other means.) The
> Text::CSV module can handle these cases, plus it can read from a file or a
> scalar and deal with broken lines and other complexities. There is also the
> Text::CSV::XS module which includes C code for speed.
>
>>
>> So I started by putting reading in the files and go one line at time,
>> putting those line in arrays and matching a specific line of interest. With
>> join I could then turn the array of interest in a scalar and print that
>> out. That is almost what I wanted (see code below):
>>
>> #! /usr/bin/perl
>> use strict;
>> use warnings;
>>
>> my $filename_data = $ARGV[0];
>> my $filename_target = $ARGV[1];
>> my $line_number = 1;
>> my @targets;
>>
>> open FILE, "<", $filename_data or die $!;
>> open TARGET, "<", $filename_target or die $!;
>
> Lexical file handles are generally better, and it helps to include the file
> name in the error message:
>
> open(my $file, '<', $filename_data) or
> die( "Can't open $filename_data for reading: $!");
>
>>
>> while (<TARGET>){
>> push (@targets, $_);
>> }
>
> You can replace the above with:
>
> my @targets = <TARGET>;
>
> You can also do this to remove the line ending characters from @targets:
>
> chomp(@targets);
>
>>
>> close (TARGET);
>>
>> while (<FILE>){
>> chomp;
>> my $line = $_;
>
> You can read directly into a scalar, so no need for the $_ variable here:
>
> while( my $line = <FILE> ) {
> chomp($line);
>
>> my @elements = split ("\t", $line);
>> my $row_name = $elements[0];
>> if ($line_number == 1){
>> my $header = join("\t", @elements);
>
> You are splitting $line, then joining it back up in $header. Why not just
> $header = $line;
>
>> print $header, "\n";
>> $line_number = 2;}
>> elsif($line_number = 2){
>
> That should be
>
> elsif( $line_number == 2 ) {
>
>> foreach (@targets){
>> chomp;
>> my $target = $_;
>> if ($row_name eq $target){
>> my $data = join("\t", @elements);
>> print $data,"\n";
>
> Once again, just use $line.
>
>> }
>> }
>> }
>> }
>>
>> close (FILE);
>>
>> Realistic, I don't want the whole row. So I started thinking about how to
>> get specific columns. I started reading on the internet and the ideas seems
>> to be placing the arrays containing the lines in a hash indexed by the row
>> names. So I did this:
>
> There are several ways to extract individual columns from a CSV line.
>
> 1. You can split the line into an array and make copies of specific elements:
>
> my @fields = split("\t",$line);
> my $name = $fields[0];
> my $address = $fields[3];
> my $zip = $fields[7];
>
> 2. You can use an array slice on the array:
>
> my( $name, $address, $zip ) = @fields[0,3,7];
>
> 3. You can use an array slice on the return list from split:
>
> my( $name, $address, $zip ) = (split("\t",$line))[0,3,7];
>
> 4. You can split the line into individual variables:
>
> my( $name, $position, $salary, $address, $street, $city, $country, $zip ) =
> split("\t",$line);
>
> 5. You can use undefs to ignore columns you don't want:
>
> my( $name, undef, undef, $address, undef, undef, undef, $zip ) =
> split("\t",$line);
>
>
>
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