减少一个惰性序列,就像一个带有Clojure条件的循环 [英] Reduce a lazy sequence like a loop with a condition in Clojure
问题描述
我有一个无限的延迟序列,产生一个前导和一个模式重复,这种序列的一个简单的例子可以在Clojure中实现:
(def infinite-lazy-sequence
(lazy-cat [4](cycle [1 2 3])))
=> (取20无限延迟序列)
(4 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1)
我想得到一个 set
的元素组成 infinite-lazy-sequence
:这是一种使用循环
实现它的方法:
code>(loop
[[head& tail] infinite-lazy-sequence
result#{}]
(if(contains?result head)
result
(recur tail(conj result head))))
=> #{1 2 3 4}
这里是问题:是否可以实现相同的结果 reduce
?使用 take-while
?
编辑:
使用clojure-1.5.1和perforate-0.2.4的基准测试结果
建议 loop-recur
实现:
60个1呼叫的60个样本中的60个。
执行时间平均值:1.054975秒
执行时间std偏差:26.316442 ms
执行时间较低分位数:1.026187秒(2.5%)
执行时间上位分辨率:1.125854秒%)
@ sw1nn reduce-reduced
:
案例:reduce-reduced
评估计数:60个2次调用的60个样本中有120个。
执行时间平均值:875.091831 ms
执行时间std偏差:19.745142 ms
执行时间较低分位数:850.871606 ms(2.5%)
执行时间上位分辨率:921.947759 ms Clojure 1.5已添加
减少以允许短路减少...
(reduce(fn [av] (av)(conj av)(reduced a)))
#{}
infinite-lazy-sequence)
=> #{1 2 3 4}
I have an infinite lazy sequence that produce a "preamble" and a "pattern repetition", a simple example of this kind of sequence could be implemented in Clojure with:
(def infinite-lazy-sequence
(lazy-cat [4] (cycle [1 2 3])))
=> (take 20 infinite-lazy-sequence)
(4 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1)
I would like to get a set
of the elements forming this infinite-lazy-sequence
, here is a way to implement it using loop
:
(loop
[[head & tail] infinite-lazy-sequence
result #{}]
(if (contains? result head)
result
(recur tail (conj result head))))
=> #{1 2 3 4}
Here is the question: is it possible to achieve the same result using reduce
? And using take-while
?
Edit:
Benchmark results using clojure-1.5.1 and perforate-0.2.4
proposed loop-recur
implementation:
Case: :loop-recur
Evaluation count : 60 in 60 samples of 1 calls.
Execution time mean : 1.054975 sec
Execution time std-deviation : 26.316442 ms
Execution time lower quantile : 1.026187 sec ( 2.5%)
Execution time upper quantile : 1.125854 sec (97.5%)
@sw1nn reduce-reduced
implementation:
Case: :reduce-reduced
Evaluation count : 120 in 60 samples of 2 calls.
Execution time mean : 875.091831 ms
Execution time std-deviation : 19.745142 ms
Execution time lower quantile : 850.871606 ms ( 2.5%)
Execution time upper quantile : 921.947759 ms (97.5%)
Clojure 1.5 added reduced
to allow shortcircuiting reduces...
(reduce (fn [a v] (if-not (a v) (conj a v) (reduced a)))
#{}
infinite-lazy-sequence)
=> #{1 2 3 4}
这篇关于减少一个惰性序列,就像一个带有Clojure条件的循环的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!