在 ruby​​ / rails 中，我如何为公共循环制作这个助手？

Question

I write this bit of code all the time, it compaires two of the same array expect if they're the same item:

items.each_with_index do | x, i |
    items.each do | y, j |
        if x.id != y.id
            #... do some things
        end
    end
end

What I'd really like to write is:

items.compare_each do | x, y, i, j |
    #... do some things
end

How would you go about writing a helper that in ruby/rails? Or even does it already exist?

Answer 1

Assuming you're trying to compare each element in a single array with every other element in that array, as your example code shows (rather than comparing two arrays with each other, as your text states), you want Array#combination , possibly in conjunction with Enumerable#each_with_index if the indexing is important:

%i{a b c d e}.each_with_index.to_a.combination(2) {|(x,i),(y,j)| p [x,y,i,j] }
[:a, :b, 0, 1]
[:a, :c, 0, 2]
[:a, :d, 0, 3]
[:a, :e, 0, 4]
[:b, :c, 1, 2]
[:b, :d, 1, 3]
[:b, :e, 1, 4]
[:c, :d, 2, 3]
[:c, :e, 2, 4]
[:d, :e, 3, 4]
=> [[:a, 0], [:b, 1], [:c, 2], [:d, 3], [:e, 4]]

The above example also makes use of argument destructuring .