有没有一种简单的方法使用LINQ to合并两个有序序列？ [英] Is there an easy way to merge two ordered sequences using LINQ?

问题描述

由于

IEnumerable<T> first;
IEnumerable<T> second;

和两个第一和第二由比较器排序 Func键＆LT; T， T，INT＆GT; ，对于平等返回0，-1时，第一条就是小和1时，第二个是小

and that both first and second are ordered by a comparer Func<T, T, int> that returns 0 for equality, -1 when the first is "smaller" and 1 when the second is "smaller".

有没有使用LINQ to的方式，使所产生的序列也由同一个比较器下令两个序列合并一个直接的方式？

我们目前正在使用的是手工制作的算法，工作，但一个直接的LINQ语句的可读性是preferable。

We're currently using a hand-crafted algorithm that works, but the readability of a straight-forward LINQ statement would be preferable.

推荐答案

您可以定义此扩展方法。类似

You could define an extension method for this. Something like

public static IEnumerable<T> MergeSorted<T>(this IEnumerable<T> first, IEnumerable<T> second, Func<T, T, int> comparer) 
{
    using (var firstEnumerator = first.GetEnumerator())
    using (var secondEnumerator = second.GetEnumerator())
    {

        var elementsLeftInFirst = firstEnumerator.MoveNext();
        var elementsLeftInSecond = secondEnumerator.MoveNext();
        while (elementsLeftInFirst || elementsLeftInSecond)
        {
            if (!elementsLeftInFirst)
            {
                    do
                    {
                        yield return secondEnumerator.Current;
                    } while (secondEnumerator.MoveNext());
                    yield break;
            }

            if (!elementsLeftInSecond)
            {
                    do
                    {
                        yield return firstEnumerator.Current;
                    } while (firstEnumerator.MoveNext());
                    yield break;
            }

            if (comparer(firstEnumerator.Current, secondEnumerator.Current) < 0)
            {
                yield return firstEnumerator.Current;
                elementsLeftInFirst = firstEnumerator.MoveNext();
            }
            else
            {
                yield return secondEnumerator.Current;
                elementsLeftInSecond = secondEnumerator.MoveNext();
            }
        }
    }
}

用法：

var s1 = new[] { 1, 3, 5, 7, 9 };
var s2 = new[] { 2, 4, 6, 6, 6, 8 };

var merged = s1.MergeSorted(s2, (a, b) => a > b ? 1 : -1).ToList();

Console.WriteLine(string.Join(", ", merged));

输出：

1, 2, 3, 4, 5, 6, 6, 6, 7, 8, 9

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