在 C# 中为 IEnumerable 实现的 F# Seq 模块? [英] F# Seq module implemented in C# for IEnumerable?

问题描述

F# 有一堆标准序列运算符，我从使用 Mathematica 的经验中逐渐了解和喜爱.F#现在引起了我的广泛关注，当它正式发布时，我打算经常使用它.

F# has a bunch of standard sequence operators I have come to know and love from my experience with Mathematica. F# is getting lots of my attention now, and when it is in general release, I intend to use it frequently.

现在，由于 F# 尚未正式发布，我无法在生产代码中真正使用它.LINQ 使用类似 SQL 的名称实现了其中一些运算符(例如，select"是map"，where"是filter")，但我找不到fold"、iter"或partition"的实现.

Right now, since F# isn't yet in general release, I can't really use it in production code. LINQ implements some of these operators using SQL-like names (e.g. 'select' is 'map', and 'where' is 'filter'), but I can find no implementation of 'fold', 'iter' or 'partition'.

有没有人见过标准序列运算符的任何 C# 实现?这是应该有人写的吗?

Has anyone seen any C# implementation of standard sequence operators? Is this something someone should write?

推荐答案

如果您仔细观察，许多 Seq 操作都有 LINQ 等效项或可以轻松派生.只是俯视 列表...

If you look carefully, many Seq operations have a LINQ equivalent or can be easily derived. Just looking down the list...

• Seq.append = Concat(IEnumerable second)

Seq.concat = SelectMany, TResult>(s => s)

Seq.distinct_by = GroupBy(keySelector).Select(g => g.First())

Seq.exists = Any(Func谓词)

Seq.mapi = Select(Func selector)

Seq.fold = Aggregate(TAccumulate seed, Func func)

List.partition 定义如下:

将集合拆分为两个集合，分别包含给定谓词返回true和false的元素

Split the collection into two collections, containing the elements for which the given predicate returns true and false respectively

我们可以使用 GroupBy 和一个二元数组作为穷人的元组来实现:

Which we can implement using GroupBy and a two-element array as a poor-man's tuple:

public static IEnumerable<TSource>[] Partition<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
{
    return source.GroupBy(predicate).OrderByDescending(g => g.Key).ToArray();
}

元素 0 保存真实值；1 持有假值.GroupBy 本质上是类固醇的分区.

Element 0 holds the true values; 1 holds the false values. GroupBy is essentially Partition on steroids.

最后，Seq.iter 和 Seq.iteri 很容易映射到 foreach:

And finally, Seq.iter and Seq.iteri map easily to foreach:

public static void Iter<TSource>(this IEnumerable<TSource> source, Action<TSource> action)
{
    foreach (var item in source)
        action(item);
}

public static void IterI<TSource>(this IEnumerable<TSource> source, Action<Int32, TSource> action)
{
    int i = 0;
    foreach (var item in source)
        action(i++, item);
}

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