How does mapcat work?

Question

I am really new to clojure! How does `mapcat work?

Answer 1

mapcat function is just a shortcut for applying concat function to the result of map function:

=> (mapcat reverse [[3 2 1 0] [6 5 4] [9 8 7]])
(0 1 2 3 4 5 6 7 8 9)

=> (apply concat (map reverse [[3 2 1 0] [6 5 4] [9 8 7]]))
(0 1 2 3 4 5 6 7 8 9)

References:

• official Clojure API docs
• clojuredocs.org website

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By using mapcat in combination with vector function you can interlace several collections:

=> (mapcat vector [1 2 3 4 5 6] [:q :w :e :r :t :y])
(1 :q 2 :w 3 :e 4 :r 5 :t 6 :y)

You'll get the same result using list function instead of vector.