Question

I have an array like this:

stuff = ["A", " ", "C", " ", "E", " ", "G"]

and I want to return an array of all the indexes where the data is a blank space say. Eg:

[1, 3, 5]

Is there a nice functional way to do this? I know there is an each_with_index method returning an Enumerable, but I couldn’t figure out how to wield it with a filter.

Edit: NVM, JUST solved it after 30 minutes of trying. Here is my method.

indexes = stuff.collect.with_index { |elem, index| index if elem == " "}.
             select { |elem| not elem.nil? }

Answer 1

Let me shorten it a bit for you:

['A', ' ', 'C', ' ', 'E', ' ', 'G'].map.with_index { |e, i| i if e == ' ' }.compact

The thing is that you can use Enumerable#compact instead of doing a select. Also, I find #map to be the more popular term, especially when you talk about functional programming, but that’s apples and oranges in the end.