Clojure provides a builtin way for easy Java Interop.
(java.util.Collections/indexOfSubList '(a b c 5 6 :foo g h) '(5 6 :foo))
;=> 3
题
Does Clojure provide any builtin way to find the position of a sub-sequence in a given sequence?
解决方案
Clojure provides a builtin way for easy Java Interop.
(java.util.Collections/indexOfSubList '(a b c 5 6 :foo g h) '(5 6 :foo))
;=> 3
其他提示
A sequence is an abstraction, not a concretion. Certain concretions that you can use through the sequence abstraction have a way to find the position of a subsequence (strings and java collections, for instance), but sequences in general don't, because the underlying concretion doesn't have to have an index.
What you can do however, is create a juxt of the element identity and an index function. Have a look at map-indexed.
Here's a naive implementation that will lazily find the position of (all) the subsequence(s) in a sequence. Just use first or take 1 to find only one:
(defn find-pos
[sq sub]
(->>
(partition (count sub) 1 sq)
(map-indexed vector)
(filter #(= (second %) sub))
(map first)))
=> (find-pos [:a :b \c 5 6 :foo \g :h]
[\c 5 6 :foo])
(2)
=> (find-pos "the quick brown fox"
(seq "quick"))
(4)
Take care that index-based algorithms generally aren't something you would do in a functional language. Unless there are good reasons you need the index in the final result, lavish use of index lookup is considered code smell.