You were close.. I fixed your code? ...Don't sort the IDs - if you want to preserve the order of the data! Also, its a fluke that the data appeared in the right order due to sort in uniqjoin().

List::Util is a core module (no installation required) - you will have to install List::MoreUtil if you want to use it. Besides being very handy functions, they are fast because they are implemented in C.

use strict;
use warnings;
use Data::Dumper;

my @IDs = qw(Apple Apple Grape Banana Banana);
my @Price = qw(5 5 2 3 4 );
my @Amount = qw(10 15 3 4 4 );

sub uniqjoin {
    my $sep=shift;
    
    my %seen;
    return join($sep, grep { !$seen{$_}++ } @_); #NO SORT  
}

my %h;

#to hash of array

my $idx =0; 
foreach my $id (@IDs)
{
    push @{$h{$id}->{price}} , $Price[$idx];
    push @{$h{$id}->{amount}}, $Amount[$idx];
    $idx++;
}
#concatenate arrays with '/'
foreach my $id (keys %h){
    $h{$id}->{price}  = uniqjoin( '/', @{$h{$id}->{price} } );
    $h{$id}->{amount} = uniqjoin( '/', @{$h{$id}->{amount}} );
}

my %seen;
my @uniqIDs = grep{!$seen{$_}++}@IDs;
#print
print join(' ', @uniqIDs) . "\n";
print join(' ' , map{ $h{$_}->{price} }  @uniqIDs ) . "\n";
print join(' ' , map{ $h{$_}->{amount} } @uniqIDs ) . "\n";

__END__
Apple Grape Banana
5 2 3/4
10/15 3 4
[download]

update: notice that keys %h does not come out in any particular order - make @uniqIDs and use that array to enforce the ordering of the data to be like in the original when you print it out - and this will wind up being faster than doing multiple "sort keys %h" anyway

There is some redundancy in the code, you could make your own uniq() function like the one in List:MoreUtil and use in join() - but why bother? Use the module and get the advantage of well debugged, fast code (should run faster than a pure Perl implementation). Of course there are some scalability/re-usability issues too - due to hard coding of price and value - but if this meets your needs - go for it!

If you use a Perl 5.12 feature like the each() function for arrays, I would put a "use 5.012;" statement in the code. Many people like me are still at 5.10.1.