`map` based on condition

Do a select first

clients.select{|c| c.type == 'tablet'}.map(&:ip)

Ruby 2.7+

Ruby 2.7 is introducing filter_map for this exact purpose. It's idiomatic and performant, and I'd expect it to become the norm very soon.

For example:

numbers = [1, 2, 5, 8, 10, 13]
enum.filter_map { |i| i * 2 if i.even? }
# => [4, 16, 20]

Here's a good read on the subject.

Hope that's useful to someone!

Answer is as simple as that:

clients.map { |client| client.ip if client.type == 'tablet' }.compact

Mapping with condition will give nils for clients which failed the condition, for that only we kept compact, which will actually flush the nil values.