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clojurereduce

Apply reduce for each element of seq

I have collection of lists and I want to apply "reduce +" for each list in collection. I think I should combine "apply", "map" and "reduce +", but I can't understand how. Example: [[1 2 3] [4 5 3] [2 5 1]] => [6 12 8]

Solution

  • No need for apply. map and reduce will work fine: 

    (map (partial reduce +) [[1 2 3] [4 5 3] [2 5 1]])

    map will call the function on each member of the list and partial simply creates a 'curried' version of reduce that expects one parameter. it could also be written like #(reduce + %) or (fn [lst] (reduce + lst))

    Update

    You could actually use apply in place of reduce here as well (just not both):

    (map (partial apply +) [[1 2 3] [4 5 3] [2 5 1]])

    Further Update

    If you have any performance concerns, see the comments on this answer for some great tips by @AlexMiller