Question

Given the following:

user> (map (fn [x] (map #(* x %) '(1 2))) '(2 3))  
((2 4) (3 6))

In clojure how can I make change this idiomatically so that the output becomes:

(2 4 3 6)

I used lists to ilustrate, but any collection is fine.

Answer 1

(mapcat (fn [x] (map #(* x %) '(1 2))) '(2 3))

Which is shorthand for:

(apply concat (map (fn [x] (map #(* x %) '(1 2))) '(2 3)))

concat concatenates collections together into one sequence. Calling it with apply allows you to pass a collection of collections to be concatenated.