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.

In reply to Re^2: Reg: Performance by sivaraman
in thread Reg: Performance by sivaraman

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.