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

Question

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

Answer 1

Just wanted to note a behavioral and performance difference for some of the solutions here. The "tie breaking" behavior of duplicate max elements:

a = [3,1,2,3]
a.each_with_index.max[1]
# => 3
a.index(a.max)
# => 0

Out of curiosity I ran them both in Benchmark.bm (for the a above):

user     system      total        real
each_with_index.max  0.000000   0.000000   0.000000 (  0.000011)
index.max  0.000000   0.000000   0.000000 (  0.000003)

Then I generated a new a with Array.new(10_000_000) { Random.rand } and reran the test:

user     system      total        real
each_with_index.max
  2.790000   0.000000   2.790000 (  2.792399)
index.max  0.470000   0.000000   0.470000 (  0.467348)

This makes me think unless you specifically need to choose the higher index max, a.index(a.max) is the better choice.