ЭЛЕКТРОННАЯ БИБЛИОТЕКА КОАПП |
Сборники Художественной, Технической, Справочной, Английской, Нормативной, Исторической, и др. литературы. |
11.2. Making Hashes of ArraysProblemFor each key in a hash, only one scalar value is allowed, but you'd like to use one key to store and retrieve multiple values. That is, you'd like the value to be a list. SolutionUse references to arrays as the hash values. Use push(@{ $hash{"KEYNAME"} }, "new value"); Then, dereference the value as an array reference when printing out the hash: foreach $string (keys %hash) { print "$string: @{$hash{$string}}\n"; } DiscussionYou can only store scalar values in a hash. References, however, are scalars. This solves the problem of storing multiple values for one key by making Here's how to give a key many values: $hash{"a key"} = [ 3, 4, 5 ]; # anonymous array Once you have a key with many values, here's how to use them: @values = @{ $hash{"a key"} }; To append a new value to the array of values associated with a particular key, use push @{ $hash{"a key"} }, $value; The classic application of these data structures is inverting a hash that has many keys with the same associated value. When inverted, you end up with a hash that has many values for the same key. This is addressed in Recipe 5.8. Be warned that this: @residents = @{ $phone2name{$number} }; causes a runtime exception under @residents = exists( $phone2name{$number} ) ? @{ $phone2name{$number} } : (); See AlsoThe section on "Hashs of Arrays" in Chapter 4 of Programming Perl and in perldsc (1); Recipe 5.8; the example "Tie Example: Make a Hash That Always Appends" in Recipe 13.15 |