In Ruby, what is the cleanest way of obtaining the index of the largest value in an array?

If a is the array, I want a.index(a.max), but something more Ruby-like. It should be obvious, but I'm having trouble finding the answer at so and elsewhere. Obviously, I am new to Ruby.

Solution 1:

For Ruby 1.8.7 or above:

a.each_with_index.max[1]

It does one iteration. Not entirely the most semantic thing ever, but if you find yourself doing this a lot, I would wrap it in an index_of_max method anyway.

Solution 2:

In ruby 1.9.2 I can do this;

arr = [4, 23, 56, 7]
arr.rindex(arr.max)  #=> 2

Solution 3:

Here is what I am thinking to answer this question :

a = (1..12).to_a.shuffle
# => [8, 11, 9, 4, 10, 7, 3, 6, 5, 12, 1, 2]
a.each_index.max_by { |i| a[i] }
# => 9