选择一个列表的所有独特的组合，没有重复，使用LINQ [英] Select all unique combinations of a single list, with no repeats, using LINQ

问题描述

我有号码的列表，我需要创建列表中的号码的每一种可能的独特的组合，而不重复使用LINQ查询。因此，举例来说，如果我有 {1，2，3} ，组合将是 1-2 ， 1-3 和 2-3 。

I have a list of numbers, and I need to create every possible unique combination of the numbers in the list, without repeats, using a LINQ query. So, for example, if I have { 1, 2, 3 }, the combinations would be 1-2, 1-3, and 2-3.

我目前使用两个为循环，就像这样：

I currently use two for loops, like so:

for (int i = 0; i < slotIds.Count; i++)
{
    for (int j = i + 1; j < slotIds.Count; j++)
    {
        ExpressionInfo info1 = _expressions[i];
        ExpressionInfo info2 = _expressions[j];

        // etc...
    }
}

是否有可能转换这两个为循环到LINQ？

Is it possible to convert these two for loops to LINQ?

感谢。

推荐答案

当然 - 你可以使用嵌入的呼叫做中的SelectMany 单呼跳过：

Sure - you can do it in a single call to SelectMany with an embedded call to Skip:

var query = slotIds.SelectMany((value, index) => slotIds.Skip(index + 1),
                               (first, second) => new { first, second });

下面是一个替代方案，不使用的非常的这样一个深奥的超载的SelectMany ：

Here's an alternative option, which doesn't use quite such an esoteric overload of SelectMany:

var query = from pair in slotIds.Select((value, index) => new { value, index })
            from second in slotIds.Skip(pair.index + 1)
            select new { first = pair.value, second };

这基本上做同样的事情，只是方式略有不同。

These do basically the same thing, just in slightly different ways.

下面是另一个选项，它是更接近原始的：

Here's another option which is much closer to your original:

var query = from index in Enumerable.Range(0, slotIds.Count)
            let first = slotIds[index] // Or use ElementAt
            from second in slotIds.Skip(index + 1)
            select new { first, second };

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