You need to work with the elements of a hash in a particular order.
Use keys to get a list of 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
}Even though you can''t directly maintain a hash in a specific order (unless you use the Tie::IxHash module mentioned in Recipe 5.7), 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";
}The sort and keys functions in perlfunc(1) and in Chapter 29 of Programming Perl; Recipe 5.7; we discuss sorting lists in Recipe 4.16