Re: Processing while reading in input

#!/usr/bin/perl

# https://perlmonks.org/?node_id=1222680

use strict;
use warnings;

while( <DATA> )
  {
  my ($cluster, $member) = split;
  print $cluster eq $member ? "\n" x ($. > 1) : ', ', $member;
  }
print "\n";

__DATA__
Osat_a    Osat_a # just one cluster member
Atha_b    Atha_b # >1 cluster member, this & next line = 2 members
Atha_b    Mtru_c
Fves_d    Fves_d # this & next 2 lines = 3 cluster members
Fves_d    Osat_e
Fves_d    Atha_f
Atha_g    Atha_g # just 1 cluster member
Osat_h    Osat_h
Osat_h    Atha_i
Mtru_j    Mtru_j # just 1 cluster member
[download]

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Re^2: Processing while reading in input by onlyIDleft (Scribe) on Sep 20, 2018 at 02:13 UTC
Thank you, tybalt89. Your code worked in terms of generating the expected output. Could you please explain in detail the following 2 lines from your code? Thank you! `my ($cluster, $member) = split; print $cluster eq $member ? "\n" x ($. > 1) : ', ', $member;` [download]	[reply] [d/l]
Re^3: Processing while reading in input by AnomalousMonk (Archbishop) on Sep 20, 2018 at 03:47 UTC
Let me presume to answer for tybalt89. `my ($cluster, $member) = split;` This depends on default behavior of split, and is equivalent to `my ($cluster, $member) = split ' ', $_;` The `' '` split pattern is a special case explained in `split` docs. `print $cluster eq $member ? "\n" x ($. > 1) : ', ', $member;` This is a bit more tricksy. From the inside out: `($. > 1)` `$.` is input line counter (update: see perlvar). `($. > 1)` evaluates to either '' (empty string) or 1 and will be 1 for every input line after the first. `"\n" x ($. > 1)` Repeats a newline zero times for the first line of input (empty string silently promoted to 0 in this special case), once for every subsequent input line. `$cluster eq $member ? Newline_or_Nada : ', '` Ternary expression. If `$cluster eq $member` true, output newline for every input line after the first (see previous item); if false, output `', '` string. `print Ternary_Expression, $member;` print result of ternary expresssion (see previous item), then `$member` string. And that's all there is to it (I think). Update: Minor wording changes. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]