ЭЛЕКТРОННАЯ БИБЛИОТЕКА КОАПП |
Сборники Художественной, Технической, Справочной, Английской, Нормативной, Исторической, и др. литературы. |
5.11. Finding Common or Different Keys in Two HashesProblemYou need to find keys in one hash that are present in another hash or keys in one hash that are not present in another. SolutionUse Find common keysmy @common = (); foreach (keys %hash1) { push(@common, $_) if exists $hash2{$_}; } # @common now contains common keys Find keys from one hash that aren't in bothmy @this_not_that = (); foreach (keys %hash1) { push(@this_not_that, $_) unless exists $hash2{$_}; } DiscussionBecause we're finding common or different keys of the hashes, we can apply our earlier array recipes for finding common or different elements to arrays of the hashes' keys. For an explanation, see Recipe 4.8. This code uses the difference technique to find non-citrus foods: # %food_color per the introduction # %citrus_color is a hash mapping citrus food name to its color. %citrus_color = ( Lemon => "yellow", Orange => "orange", Lime => "green" ); # build up a list of non-citrus foods @non_citrus = (); foreach (keys %food_color) { push (@non_citrus, $_) unless exists $citrus_color{$_}; } See AlsoThe "Variables" section of Chapter 2 of Programming Perl; the |