clojure - 无法进行排序映射并一起应用工作

Question

我在使用带有 sorted-map-by 和 apply 的自定义比较器时遇到问题。如何使下面的表达式起作用-

(apply sorted-map-by > {1 "ab" 3 "cs" 2 "vs"})

我得到以下异常 -

IllegalArgumentException 没有为键提供值：[3 "cs"] clojure.lang.PersistentTreeMap.create (PersistentTreeMap.java:87)

Answer 1

Assuming you are wanting to sort on keys with an existing map, you could use into:

(into (sorted-map-by >) {1 "ab" 3 "cs" 2 "vs"})

This works because (sorted-map-by >) returns an empty sorted map, so using functions like into and assoc will work as expected while the map maintains the sorted order.

;=> {3 "cs", 2 "vs", 1 "ab"}

The sorted-map-by function works on flat arguments:

(sorted-map-by > 1 "ab" 3 "cs" 2 "vs")
;=> {3 "cs", 2 "vs", 1 "ab"}

Applying it to this map would give an odd number of pairs:

(apply list {1 "ab" 3 "cs" 2 "vs"})
;=> ([1 "ab"] [2 "vs"] [3 "cs"])

And it is trying to make every other one a value to a preceding key, hence the error.

Answer 2

apply如果在编译时不知道要传递给函数的参数数量，您将使用. 所以最好的方法是使用

(into (sorted-map-by >) {1 "ab" 3 "cs" 2 "vs"})