%hash = ( 
    name  => 'Rhesa',
    fruit => 'Mango',
    dog   => 'Spot',
    cat   => 'Stofje',
);
[download]

%pets = (
    dog   => 'Spot',
    cat   => 'Stofje',
);
[download]

The most obvious answer would be:

%pets = (
    dog => $hash{dog},
    cat => $hash{cat},
);
[download]

That's just wrong. Unfortunately, I see it quite often in my code base, most notably when creating Class::DBI objects².

Of course, there's the two-stage approach using slices:

my @animals = qw( dog cat );
my %pets;
@pets{ @animals } = @hash{ @animals };
[download]

But I don't like that it requires a temporary variable.

The next best thing I could think of is:

%pets = map { $_ => $hash{$_} }
        qw( dog cat );
[download]

But that shows too much machinery for my taste. It's like having to start your car with a crank instead of a key or button.

I'm gravitating towards writing a function for it:

sub hash_slice {
    my ($hr, @k) = @_;
    return map { $_ => $hr->{$_} } @k;
}

# or using a slice (might be more efficient, but doesn't read as nicel
+y)
sub hash_slice {
    my ($hr, @k) = @_;
    my %ret;
    @ret{@k} = @$hr{@k};
    return %ret;
}

# use like this:
%pets = hash_slice( \%hash, qw( dog cat ) );
[download]

Is that the best we can do?

I'm importing data from a csv file into a database. The csv file is highly denormalized, while the database is structured nicely. My csv parser returns a hash for each line of data, so I need to store parts of this hash into different tables.

The file has these columns (and more):

@headers = qw(
    firstname lastname
    address_line1 address_line2 city zip state country
    order_number
    title bookcode isbn
    quantity
);
[download]

I need to store this data using Class::DBI classes like Customer, Address, Title, Edition, Order, Orderline etc. So some of these calls look like:

# %orderline comes from the csv
my $customer = Customer->find_or_create({
    firstname => $orderline{firstname},
    lastname  => $orderline{lastname},
});
[download]

And so on and so forth. It's a pain to read, and maintain.