如何从阵列中获得所有可能的组合？

Question

我有一个Type数组，我想为类型生成所有可能的组合。即:(假设只有int，bool和string）

int / bool / string / int，bool / int，string / int，bool，string / int，string，bool / etc.

我在这里看到Eric Lippert的答案：Generating all Possible Combinations并且正在使用他的方法，但是我很难修改它以使用Type数组而不是string / int。绊倒我的部分是“Enumerable.Range（）”和最后一部分的功能lamba。

这是我尝试但未编译的原因，因为x是int而不是类型。

return from cpLine in CartesianProduct(
       from type in types select Enumerable.Range(1, types.Length))
       select cpLine.Zip(types, (x1, x2) => new Tuple<Type, Type>(x1, x2));

Answer 1

你可以这样使用CartesianProduct：

var types = new List<Type>() { typeof(int), typeof(bool), typeof(string) };
var result = Enumerable.Range(1, types.Count())
                       .Select(x => types.AsEnumerable()).CartesianProduct().ToList();

我想你有CartesianProduct创建的Eric Lippert扩展方法：

public static class Extensions
{
    public static IEnumerable<IEnumerable<T>> CartesianProduct<T>(this IEnumerable<IEnumerable<T>> sequences)
    {
        IEnumerable<IEnumerable<T>> emptyProduct = new[] { Enumerable.Empty<T>() };
        return sequences.Aggregate(
            emptyProduct,
            (accumulator, sequence) =>
                from accseq in accumulator
                from item in sequence
                select accseq.Concat(new[] { item })
            );
    }
}

这是输出：

01: Int32, Int32, Int32
02: Int32, Int32, Boolean
03: Int32, Int32, String
04: Int32, Boolean, Int32
05: Int32, Boolean, Boolean
06: Int32, Boolean, String
07: Int32, String, Int32
08: Int32, String, Boolean
09: Int32, String, String
10: Boolean, Int32, Int32
11: Boolean, Int32, Boolean
12: Boolean, Int32, String
13: Boolean, Boolean, Int32
14: Boolean, Boolean, Boolean
15: Boolean, Boolean, String
16: Boolean, String, Int32
17: Boolean, String, Boolean
18: Boolean, String, String
19: String, Int32, Int32
20: String, Int32, Boolean
21: String, Int32, String
22: String, Boolean, Int32
23: String, Boolean, Boolean
24: String, Boolean, String
25: String, String, Int32
26: String, String, Boolean
27: String, String, String

编辑

---

要获得具有IEnumerable<T>中所有可能项目数的所有可能输出，您可以添加此扩展方法：

public static IEnumerable<IEnumerable<T>> GetAllPossibleCombinations<T>(this IEnumerable<T> source)
{
    var result = new List<IEnumerable<T>>().AsEnumerable();
    for (int i = 1; i <= source.Count(); i++)
    {
        var intermediateResult = Enumerable.Range(1, i)
                .Select(x => source.AsEnumerable()).CartesianProduct();
        result = result.Union(intermediateResult);
    }
    return result;
}

然后以这种方式使用它：

var types = new List<Type>() { typeof(int), typeof(bool), typeof(string) };
var result = types.GetAllPossibleCombinations();

这是输出：

01: Int32
02: Boolean
03: String
04: Int32, Int32
05: Int32, Boolean
06: Int32, String
07: Boolean, Int32
08: Boolean, Boolean
09: Boolean, String
10: String, Int32
11: String, Boolean
12: String, String
13: Int32, Int32, Int32
14: Int32, Int32, Boolean
15: Int32, Int32, String
16: Int32, Boolean, Int32
17: Int32, Boolean, Boolean
18: Int32, Boolean, String
19: Int32, String, Int32
20: Int32, String, Boolean
21: Int32, String, String
22: Boolean, Int32, Int32
23: Boolean, Int32, Boolean
24: Boolean, Int32, String
25: Boolean, Boolean, Int32
26: Boolean, Boolean, Boolean
27: Boolean, Boolean, String
28: Boolean, String, Int32
29: Boolean, String, Boolean
30: Boolean, String, String
31: String, Int32, Int32
32: String, Int32, Boolean
33: String, Int32, String
34: String, Boolean, Int32
35: String, Boolean, Boolean
36: String, Boolean, String
37: String, String, Int32
38: String, String, Boolean
39: String, String, String