How do I find keys in my hash to map to elements that match a condition?

Question

I have a hash that maps integers to arrays. For example

{1 => [\"abc\"], 2 => [\"ccc\", \"ffffd\"]}

How do I get all the keys from my hash

Answer 1

{1 => ["abc"], 2 => ["ccc", "ffffd"]}.select{|_, a| a.length > 1}.keys
# => [2]