A couple months ago, there was a discussion in this group about the
functions max and min and making them work with data types other than
numbers. I was toying around tonight, and I wrote the following
functions.
(defn- boundary
[compare-fn f & args]
(reduce (fn [a b] (if (compare-fn (compare (f b) (f a)))
b
a)) args))
(defn greatest-by
"Return the argument for which f returns the greatest value."
[f & args]
(apply boundary pos? f args))
(defn greatest
"Return the greatest argument."
[& args]
(apply greatest-by identity args))
(defn least-by
"Return the argument for which f returns the smallest value."
[f & args]
(apply boundary neg? f args))
(defn least
"Return the smallest element."
[& args]
(apply least-by identity args))
user> (greatest 1 3 2)
3
user> (greatest "foo" "bar" "baz")
"foo"
user> (greatest-by count "foo" "bar" "abccb")
"abccb"
user> (least 1 3 2)
1
user> (least "foo" "bar" "baz")
"bar"
user> (least-by count "foo" "bar" "abccb")
"foo"
user>
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