use Data::Dumper;

use strict;

my $var = [
	{
		'city' => 'New York',
		'name' => 'Bill'
	},
	{
		'city' => 'New York',
		'name' => 'Ronald'
	},
	{
		'city' => 'Boston',
		'name' => 'George'
	}
];

my %result;
push @{$result{$_->{city}}}, $_->{name} foreach (@$var);

print Dumper(\%result);