如何在数组的所有元素上应用函数并在clojure中将结果作为数组？

Question

generally i want to know when we have array of object that have some property can same the "Object Literal in JavaScript" can calculated with specific function. i want to create that property for my array in clojure to apply some calculation on them such as sorting or more simpler finding maximum according to that property.for example how try find maximum in this example?

(def aSqh (fn [x] (* x x)))
(def maSqh (max (apply aSqh [1 2 3 4])))

the have error that output is object and not number

Answer 1

You seem to be thinking of a mapping operation (take a function of one argument and a collection, replace every element with the result of the function on that element), which in Clojure is called map . apply is a function for plumbing collections into functions as if they were given each element as a separate argument. Usually you want to use it with variadic functions (ie functions such as max , that take a variable number of arguments). For instance

(def maSqh (apply max (map aSqh [1 2 3 4]))) ;;=> 16

If you want to preserve the datatype of a collection after performing a mapping, you can use into and empty :

(defn preserving-map [f coll]
  (into (empty coll) (map f coll)))

(preserving-map aSqh [1 2 3 4]) ;;=>[1 4 9 16]
(preserving-map aSqh #{1 2 3 4}) ;;=> #{1 4 9 16}

but this removes the (useful) laziness that map usually gives us. For the particular case of vectors (like [1 2 3 4]), this use case is common enough that there is mapv which eagerly performs mappings and puts them into a vector.