Index of the first non-nil value in an array

Question

What is the best way (in terms of idiom and efficiency) to find the index of the first value other than nil in the array?

I came up with first_non_null_index = array.index(array.dup.compact[0])... but is there a better way?

Answer 1

Ruby 1.9 has a method find_index:

ruby-1.9.1-p378 > [nil, nil, false, 5, 10, 20].find_index { |x| not x.nil? } # detect false values
 => 2 
ruby-1.9.1-p378 > [nil, nil, false, 5, 10, 20].find_index { |x| x }
 => 3 

find_indexseems to be available in backports if needed in Ruby before 1.8.7.

Answer 2

I think the best answer is only in the question. Only change

first_non_null_index = (array.compact.empty?) "No 'Non null' value exist" :  array.index(array.dup.compact[0]

Consider the following example.

array = [nil, nil, nil,  nil,  nil]
first_non_null_index = array.index(array.dup.compact[0]) #this will return '0' which is wrong