在 Linq (C#) 中动态交叉连接多个不同大小的集合 [英] Dynamically cross-join multiple different-size collections together in Linq (C#)

问题描述

我有未知数量的桶(集合)，每个桶都有未知数量的实体

I have an unknown number of buckets(collections), and each bucket having an unknown number of entities

我需要生成所有实体的笛卡尔积，以便我最终得到一个包含实体数组的集合，并且在每个数组中，每个存储桶都有 1 个代表.

I need to produce a cartesian product of all the entities, so that I endup with a single COLLECTION that has ARRAYS of entities and in each array, there is 1 representetive from EVERY bucket.

因此，如果我有 5 个桶 (B1..B5)，并且桶 B1、B2 各有 1 个项目，而桶 B3、B4 和 B5 各有 4、8 和 10 个项目，我将收集320个数组，每个数组有5个元素.

So that if I have 5 buckets (B1..B5), and buckets B1, B2 have 1 item each, and bucket B3, B4 and B5 have 4, 8 and 10 items each, I'll have a collection of 320 arrays, and each array will have 5 items.

这里唯一愚蠢的问题是，在开发时，桶的大小和桶的数量都是未知的.

The only stupud issue here, is that both size of buckets and number of buckets is unknown at development time.

性能在这里并不是特别重要，因为大多数时候，我的桶只有 1 个实体，而且很少有我的一些桶会包含 20-30 个项目的情况......我通常会有 5-30 个桶

Performance is not super important here, as most of the time, my buckets will have only 1 entity, and only rarely will there be times when some of my buckets will contain 20-30 items...and I'll usually have 5-30 buckets

我很想以某种方式在这里使用 linq，但是当我试图想象这将如何工作时，我的大脑正在被炸毁

I'd love to utilize linq here in someway, but my brain is getting fried as I try to imagine how this would work

推荐答案

您可以创建如下扩展方法:

You could create an extension method like the following:

public static class EnumerableExtensions
{
    public static IEnumerable<TValue []> Permutations<TKey, TValue>(this IEnumerable<TKey> keys, Func<TKey, IEnumerable<TValue>> selector)
    {
        var keyArray = keys.ToArray();
        if (keyArray.Length < 1)
            yield break;
        TValue [] values = new TValue[keyArray.Length];
        foreach (var array in Permutations(keyArray, 0, selector, values))
            yield return array;
    }

    static IEnumerable<TValue []> Permutations<TKey, TValue>(TKey [] keys, int index, Func<TKey, IEnumerable<TValue>> selector, TValue [] values)
    {
        Debug.Assert(keys.Length == values.Length);

        var key = keys[index];
        foreach (var value in selector(key))
        {
            values[index] = value;
            if (index < keys.Length - 1)
            {
                foreach (var array in Permutations(keys, index+1, selector, values))
                    yield return array;
            }
            else
            {
                yield return values.ToArray(); // Clone the array;
            }
        }
    }
}

举个例子，它可以像这样使用:

As an example, it could be used like:

    public static void TestPermutations()
    {
        int [][] seqence = new int [][]
        {
            new int [] {1, 2, 3},
            new int [] {101},
            new int [] {201},
            new int [] {301, 302, 303},
        };

        foreach (var array in seqence.Permutations(a => a))
        {
            Debug.WriteLine(array.Aggregate(new StringBuilder(), (sb, i) => { if (sb.Length > 0) sb.Append(","); sb.Append(i); return sb; }));
        }
    }

并产生以下输出:

1,101,201,301
1,101,201,302
1,101,201,303
2,101,201,301
2,101,201,302
2,101,201,303
3,101,201,301
3,101,201,302
3,101,201,303

这就是你想要的吗?

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