Question

I want to find the minimum element (at any level) in a non-linear list (edit: a tree), in Lisp. I wrote something like:

rootobj.get("").getAsJsonArray();

But, it's not working (because of that condition for non-numerical atoms, I guess...). Does anyone have, any idea how to fix this code? Thanks in advance.

Answer 1

您的numberp案例永远不会执行，因为atom案例首先被测试，而数字是原子。所以每个数字都被99999取代。先放numberp个案例。

您的代码的另一个问题是，如果树中的最小数字大于99999，它将找不到最小的数字。要修复它而不更改代码太多，您需要自己的版本{{1 }}支持无限的表示：

min

然后，将(defun inf-min (a b) (cond ((eq a :infinity) b) ((eq b :infinity) a) ((< a b) a) (t b)))替换为min，将99999替换为inf-min。

Answer 2

使用99999实际上是一种黑客攻击（不是好的黑客攻击），请不要这样做。使用:infinity稍微好一些，但是，在提供空列表时，您是否希望结果为:infinity？ loop方法更好，但是当列表为空时，最小化返回0，这通常不是我们想要的。

对于零值，最小函数未定义，因此我将定义tree-min函数，其中当树不包含数字时，nil中的结果为(defun tree-min (tree) (typecase tree ;; base case with numbers (number tree) ;; string are sequences too, but don't iterate over them. (string nil) ;; vectors and lists (sequence (reduce (lambda (m e) (let ((em (tree-min e))) (or (and m em (min em m)) ; Eminem? em))) tree :initial-value nil))))。像这样：

(tree-min #(3 2 nil (2 1 -20) 100 20 ))
=> -20

(tree-min nil)
=> nil

(tree-min '(a 20))
=> 20

该函数以静默方式跳过任何非数字元素。以下是一些例子：

Individ <- data.frame(Participant = c("Bill", "Bill", "Bill", "Bill", "Bill", "Bill", "Jane", "Jane", "Jane", "Jane", 
                                      "Jane", "Jane", "Jane", "Jane", "Jane", "Jane", "Jane", "Jane", "Bill", "Bill", "Bill", "Bill", "Bill", "Bill"),  
                      Time = c(1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6),
                      Condition = c("Placebo", "Placebo", "Placebo", "Placebo", "Placebo", "Placebo", "Expr", "Expr", "Expr", "Expr", "Expr", "Expr", 
                                    "Placebo", "Placebo", "Placebo", "Placebo", "Placebo", "Placebo", "Expr", "Expr", "Expr", "Expr", "Expr", "Expr"),
                      Location = c("Home", "Home", "Home", "Home", "Home", "Home", "Home", "Home", "Home", "Home", "Home", "Home", "Home", "Home", "Home", "Home", "Home", "Home", 
                                   "Away", "Away", "Away", "Away", "Away", "Away"),
                      Power = c(400, 250, 180, 500, 300, 450, 600, 512, 300, 500, 450, 200, 402, 210, 130, 520, 310, 451, 608, 582, 390, 570, 456, 205))

在实践中，您可以概括此函数以采用extremum之类的比较函数。

Answer 3

(defun minimum (tree)
    (loop for item in tree
         if (consp item) minimize (minimum item)
         else if (numberp item) minimize item))

Minimum element in a tree

3 个答案: