building a hash from a string - perl

Question

I have the below string on perl :
my $string = xyz;1;xyz;2;a;2;b;2
i want to build a hash after for this string like below :
my #array =split /;/,$string;
$hash{xyz} =(1,2);
$hash{b}=(2);
$hahs{a}=(2);
what is the perl way to do this?

Answer 1

my $string = "xyz;1;xyz;2;a;2;b;2";
my %hash;
push #{$hash{$1}}, $2 while $string =~ s/^(\w+);(\d+);?//g;
Actually
push #{$hash{$1}}, $2 while $string =~ m/(\w+);(\d+);?/g;
would be better, since that doesn't eat up your original string.

Answer 2

Assuming you want the multiple values for the same key to be an array reference, then one way to do it is like this:
my #values = split /;/, $string;
my %hash;
while( #values ) {
my $key = shift #values;
my $val = shift #values;
if ( exists $hash{$key} && !ref $hash{$key} ) {
# upgrade to arrayref
$hash{$key} = [ $hash{$key}, $val ];
} elsif ( ref $hash{$key} ) {
push #{ $hash{$key} }, $val;
} else {
$hash{$key} = $val;
}
}
With your data, this will result in a structure like
{
'a' => '2',
'b' => '2',
'xyz' => [
'1',
'2'
]
};

Answer 3

Drats: You have repeating keys... I wanted to do something with map or grep.
This is fairly simple to understand:
my $string = "xyz;1;xyz;2;a;2;b;2";
my #array = split /;/ => $string;
my %hash;
while (#array) {
my ($key, $value) = splice #array, 0, 2;
$hash{$key} = [] if not exists $hash{$key};
push #{$hash{$key}}, $value;
}
This program will work even if the key is not together in your string. For example, the following will work even though xyz is separated by the other value pairs:
my $string = "xyz;1;a;2;b;2;xyz;2";
I am assuming that $hash{b}=(2); means you want the value of $hash{b} to be a reference to a single member array. Is that correct?

Answer 4

Probably the easiest (standard) way to do this is List::MoreUtils::natatime
use List::MoreUtils qw<natatime>;
my $iter = natatime 2 => split /;/, 'xyz;1;xyz;2;a;2;b;2';
my %hash;
while ( my ( $k, $v ) = $iter->()) {
push #{ $hash{ $k } }, $v;
}
However abstracting out the parts that I would probably want to do again...
use List::MoreUtils qw<natatime>;
sub pairs {
my $iter = natatime 2 => #_;
my #pairs;
while ( my ( $k, $v ) = $iter->()) {
push #pairs, [ $k, $v ];
}
return #pairs;
}
sub multi_hash {
my %h;
push #{ $h{ $_->[0] } }, $_->[1] foreach &pairs;
return wantarray ? %h : \%h;
}
my %hash = multi_hash( split /;/, 'xyz;1;xyz;2;a;2;b;2' );