Sorting a Hash
Problem
You need to work with the elements of a hash in a particular order.
Solution
Use
keys
to get a list of
the keys, then sort them based on the ordering you
want:
# %HASH is the hash to sort
@keys = sort { criterion() } (keys %hash);
foreach $key (@keys) {
$value = $hash{$key};
# do something with $key, $value
}Discussion
Even though you can’t directly maintain a hash in a specific order (unless you use the Tie::IxHash module mentioned in Section 5.6), you can access its entries in any order.
This technique offers many variations on the same basic mechanism:
You extract the keys, reorder them using the sort
function, and then process the entries in the new order. All the
sorting tricks shown in Chapter 4, can be used
here. Let’s look at some applications.
The following code simply uses sort to order the
keys alphabetically:
foreach $food (sort keys %food_color) {
print "$food is $food_color{$food}.\n";
}This sorts the keys by their associated values:
foreach $food (sort { $food_color{$a} cmp $food_color{$b} }
keys %food_color)
{
print "$food is $food_color{$food}.\n";
}This sorts by length of the values:
@foods = sort { length($food_color{$a}) <=> length($food_color{$b}) }
keys %food_color;
foreach $food (@foods) {
print "$food is $food_color{$food}.\n";
}See Also
The sort and keys functions in
perlfunc(1) and in Chapter 3 of
Programming Perl; Section 5.6; we discuss sorting lists in Section 4.15