F＃Array.tryFindIndex从索引开始搜索

Question

我想知道是否有一个便宜的（性能明智的）选项来搜索从索引开始满足某些条件的数组元素的索引？

Array.tryFindIndex方法没有参数startIndex。我可以做Array.skip（n）然后在那里搜索，但是创建一个仅用于搜索的数组似乎很昂贵。我该怎么做呢？

我看了一下List也没有那个说法。我需要在...期间使用吗？有更好的方法吗？

Answer 1

The base libraries try to provide functions for your convenience but they cannot possibly anticipate all use cases. Nothing wrong with writing your own if need be:

module Array =
    let tryFindIndexFrom i p (a : _ []) =
        let rec loop k =
            if k >= a.Length then None
            elif p a.[k] then Some k
            else loop (k + 1)
        if i < 0 then None else loop i

EDIT: p is the predicate testing the array elements. tryFindIndexFrom has the same signature as tryFindIndex but with the starting index added as first parameter.

EDIT 2: Added test for k < 0 for fool-proof usage.

EDIT 3: Moved test for k < 0 out of the loop as it needs to be checked only once.