Clojure中最高键的返回值 [英] Return value of highest key in Clojure

问题描述

我正在使用这两组键值对，它们由另一个函数返回。我想写一个函数，总是找到最高的键，并返回其对应的值。在这个例子中，我会返回2，因为499是最高的键。我使用的数据是

I'm working with these two groups of key value pairs, which is being returned by another function. I'd like to write a function that will always find the highest key and return its corresponding value. In this example, I'd be returning 2 because 499 is the highest key. The data that I am working with is

({-99 0, 99 0} {-99 2, 499 2})

当我调用

   (type ({-99 0, 99 0} {-99 2, 499 2}))

b $ b

在负责返回数据的函数中，我回到了

Within the function that is responsible for returning that data it, I get back

 (clojure.lang.PersistentTreeMap clojure.lang.PersistentTreeMap)

我希望有所帮助。谢谢！

I hope that helps. Thanks!

推荐答案

此函数将返回一个Clojure排序映射的最右边的条目$ c> clojure.lang.PersistentTreeMap ）在对数时间：

This function will return the rightmost entry of a Clojure sorted map (the built-in implementation is called clojure.lang.PersistentTreeMap) in logarithmic time:

(defn rightmost
  "Takes a Clojure sorted map sm and returns the entry at the greatest
  key (as determined by sm's comparator)."
  [sm]
  (first (rseq sm)))

示例：

(rightmost (sorted-map 1 1 2 2 3 3))
;= [3 3]

然后，您可以使用 val 函数取出值。

You can then fish out the value using the val function.

所有 max-key / apply max - 以线性时间工作改为。不用说，这是一个巨大的区别。

All the max-key / apply max-based solutions work in linear time instead. Needless to say, it's a huge difference.

如果另一个函数可以说服返回 data.avl maps，您可以使用 nth 在对数时间的任何索引处访问元素：

If the other function could be convinced to return data.avl maps instead, you could access the element at any index in logarithmic time using nth:

;; works for data.avl sorted maps, not the built-ins
(nth (avl/sorted-map 1 1 2 2 3 3) 2)
;= [3 3]

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