if exist a hash key add the new value to existing value - perl

Question

I have a hash structure and I want to add new value to the existing value (not update with new value ).
here is my code.
use strict;
use warnings;
my %hash;
while(<DATA>){
my $line=$_;
my ($ID)=$line=~/ID=(.*?);/;
#make a hash with ID as key
if (!exists $hash{$ID}){
$hash{$ID}= $line;
}
else{
#add $line to the existing value
}
}
for my $key(keys %hash){
print $key.":".$hash{$key}."\n";
}
__DATA__
ID=13_76; gi|386755343
ID=13_75; gi|383750074
ID=13_75; gi|208434224
ID=13_76; gi|410023515
ID=13_77; gi|499086767

Answer 1

else{
$hash{$ID} .= $line;
}

Answer 2

All you need is $hash{$ID} .= $line;. No if-elses.
If there's no key $ID in the hash it would create one and concatenate $line to empty string, resulting exactly what you need.

Answer 3

You should store your data in a hash of arrays:
#!/usr/bin/env perl
use strict;
use warnings;
# --------------------------------------
use charnames qw( :full :short );
use English qw( -no_match_vars ); # Avoids regex performance penalty
use Data::Dumper;
# Make Data::Dumper pretty
$Data::Dumper::Sortkeys = 1;
$Data::Dumper::Indent = 1;
# Set maximum depth for Data::Dumper, zero means unlimited
local $Data::Dumper::Maxdepth = 0;
# conditional compile DEBUGging statements
# See http://lookatperl.blogspot.ca/2013/07/a-look-at-conditional-compiling-of.html
use constant DEBUG => $ENV{DEBUG};
# --------------------------------------
my %HoA = ();
while( my $line = <DATA> ){
if( my ( $ID ) = $line =~ m{ ID \= ([^;]+) }msx ){
push #{ $HoA{$ID} }, $line;
}
}
print Dumper \%HoA;
__DATA__
ID=13_76; gi|386755343
ID=13_75; gi|383750074
ID=13_75; gi|208434224
ID=13_76; gi|410023515
ID=13_77; gi|499086767