Merging hashes in perl - perl

Question

I am trying to merge two hashes. Well, I am able to merge, but the output is not the way I want it to be:
Here is my code:
my %friend_list = (
Raj => "Good friend",
Rohit => "new Friend",
Sumit => "Best Friend",
Rohini => "Fiend",
Allahabad => "UttarPradesh",
);
my %city = (
Bangalore => "Karnataka",
Indore => "MadhyaPradesh",
Pune => "Maharashtra",
Allahabad => "UP",
);
my %friends_place = ();
my ($k, $v);
foreach my $ref (\%friend_list, \%city) {
while (($k,$v) = each (%$ref)) {
if (exists $ref{$k}) {
print"Warning: Key is all ready there\n";
next;
}
$friends_place{$k} = $v;
}
}
while (($k,$v) = each (%friends_place)) {
print "$k = $v \n";
}
From this o/p is
Raj=Good friend
Indore=MadhyaPradesh
Rohit=new Fiend
Bangalore=Karnataka
Allahabad=UttarPradesh
Sumit=Best Friend
Pune=Maharashtra
Rohini =Fiend
But I want to print %friend_list first followed by %city.
Another thing which I was trying to do is, if there is any duplicate key, then it should give me a warning message. But it is not giving me any message. As we can see here, we have Allahabad in both hash.
Thanks

Answer 1

Try with:
my %firend_list = (
Raj => "Good friend",
Rohit => "new Fiend",
Sumit => "Best Friend",
Rohini => "Fiend",
Allahabad => "UttarPradesh",
);
my %city = (
Bangalore => "Karnataka",
Indore => "MadhyaPradesh",
Pune => "Maharashtra",
Allahabad => "UP",
);
#merging
my %friends_place = ( %friend_list, %city );
And, for warnings:
foreach my $friend( keys %friend_list ){
print"Warning: Key is all ready there\n" if $friend ~~ [ keys %city ];
}

Answer 2

The line if (exists $ref{$k}) { is wrong and you can see it if you're putting use strict; use warnings; at the begining of the script.
Moreover this line should be if (exists $friends_place{$k}) { to produce the message about duplicate keys.

Answer 3

As hashes are unordered, you need to use an array to store the ordering:
my %friends_place = (%firend_list, %city);
my #friends_place_keyorder = ((keys %firend_list), (keys %city));
if ((scalar keys %friends_place) != (scalar #friends_place_keyorder)) {
print 'duplicate key found';
}
foreach (#friends_place_keyorder) {
print "$_ = $friends_place{$_}\n";
}
EDIT: my original solution in python, left here for historical purpose:
As hashes are unordered, you need to use an array to store the ordering. I don't know perl, so the following code is python (should be fairly straightforward to translate to perl):
friend_list = ...
city = ...
friends_place = dict(friend_list.items() + city.items())
friends_place_keyorder = friend_list.keys() + city.keys()
# detect duplicate keys by checking their lengths
# if there is duplicate then the hash would be smaller than the list
if len(friends_place) != len(friends_place_keyorder):
print "duplicate key found"
# iterate through the list of keys instead of the hashes directly
for k in friends_place_keyorder:
print k, friends_place[k]