in reply to Re: Reg: Performance
in thread Reg: Performance

Thank you Salva. Now I have a code like 

my %b;
while (DUMP_B) {
  chomp;
  my ($id, $ac) = split /\|/, $_;
  push @{$b{$id}}, $ac;
}
my $readID;
while(defined($readID = DUMP_A)){
  #chomp;
  $readID =~ s!\s+!!g;
  my $ac = $b{$readID} || [];
  #print "$readID: ", join(', ', @$ac), "\n";
  my $arrSize = scalar @$ac;
  if($arrSize > 0 ){
    for (my $i = 0; $i < $arrSsize ; $i++) {
        print OUTPUT "$readID|@$ac[$i] \n";
    }
  }
}

[download]
This gives the expected output. Could you please explain me on 'my $ac = $b{$readID} || [];' Thank you once again and for all the Monks.

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Re^3: Reg: Performance
by salva (Canon) on Oct 29, 2010 at 08:14 UTC 
    $b{$readID} || []

    [download]
    When there are no entries for $readID in DUMP_B, $b{$readID} becomes undef, appending || [] handles this special case replacing undef by a reference to an empty array so that we can dereference it later as @$ac.

    A simpler version of the code follows: 

    my %b;

open(B, "<" . DUMP_B) || die("Could not open file \n");
while (<B>) {
  chomp;
  my ($id, $ac) = split /\|/, $_;
  push @{$b{$id}}, $ac;
}

open( OUTPUT, '>', 'INACTIVE_LIST' ) || die "Could not write to file\n
+";
open(A, "<" . DUMP_A) || die("Could not open file \n");
while(<A>) {
  chomp;
  s/\s+//g;
  if ($b{$_}) {
    for my $ac (@{$b{$_}}) {
      print OUTPUT "$_|$ac\n"
    }
  }
}

    [download]
    BTW, when programming in Perl it is very unusual to use C-like (or Java-like) for loops. Instead, for (@array) { ... } and for (0..$top) { ... } are used.
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      Thank you Salva for your help and also for this clarification.

      - Thank you all Monks for spent your valuable time on this.
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