如何通过两个IEnumerables同时循环？ [英] How to iterate through two IEnumerables simultaneously?

问题描述

我要的enumerables 的IEnumerable＆LT; A＆GT; list1的和的IEnumerable＆LT; B＆GT;列表2 ，并希望通过他们同时迭代，如：

I have to enumerables IEnumerable<A> list1 and IEnumerable<B> list2 and would like to iterate through them simultaneously like:

foreach((a, b) in (list1, list2)) {
  // use a and b
}

如果它们不包含相同数量的元素，一个异常应该抛出。

If they do not contain the same number of elements, an exception should be thrown.

什么是做到这一点的最好方法是什么？

What is the best way to do this?

推荐答案

下面是该操作的实现，通常被称为邮编：

Here's an implementation of this operation, typically called Zip:

using System;
using System.Collections.Generic;

namespace SO2721939
{
    public sealed class ZipEntry<T1, T2>
    {
        public ZipEntry(int index, T1 value1, T2 value2)
        {
            Index = index;
            Value1 = value1;
            Value2 = value2;
        }

        public int Index { get; private set; }
        public T1 Value1 { get; private set; }
        public T2 Value2 { get; private set; }
    }

    public static class EnumerableExtensions
    {
        public static IEnumerable<ZipEntry<T1, T2>> Zip<T1, T2>(
            this IEnumerable<T1> collection1, IEnumerable<T2> collection2)
        {
            if (collection1 == null)
                throw new ArgumentNullException("collection1");
            if (collection2 == null)
                throw new ArgumentNullException("collection2");

            int index = 0;
            using (IEnumerator<T1> enumerator1 = collection1.GetEnumerator())
            using (IEnumerator<T2> enumerator2 = collection2.GetEnumerator())
            {
                while (enumerator1.MoveNext() && enumerator2.MoveNext())
                {
                    yield return new ZipEntry<T1, T2>(
                        index, enumerator1.Current, enumerator2.Current);
                    index++;
                }
            }
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            int[] numbers = new[] { 1, 2, 3, 4, 5 };
            string[] names = new[] { "Bob", "Alice", "Mark", "John", "Mary" };

            foreach (var entry in numbers.Zip(names))
            {
                Console.Out.WriteLine(entry.Index + ": "
                    + entry.Value1 + "-" + entry.Value2);
            }
        }
    }
}

要让它抛出一个异常，如果只是顺序的一个跑出来的价值观，改变while循环这样：

To make it throw an exception if just one of the sequences run out of values, change the while-loop so:

while (true)
{
    bool hasNext1 = enumerator1.MoveNext();
    bool hasNext2 = enumerator2.MoveNext();
    if (hasNext1 != hasNext2)
        throw new InvalidOperationException("One of the collections ran " +
            "out of values before the other");
    if (!hasNext1)
        break;

    yield return new ZipEntry<T1, T2>(
        index, enumerator1.Current, enumerator2.Current);
    index++;
}

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