[英]Best way to enumerate all combinations
假设我有以下任何顺序的列表:
S1
R1
R2
S2
S3
我需要创建一个列表,其中每个“S”包含每个“R”组合
输出:
S1 => R1
S1 => R2
S2 => R1
S2 => R2
S3 => R1
S3 => R2
实现这一目标的最佳方法是什么? 谢谢
尝试:
var byPrefix = list.GroupBy(i => i.First()).ToDictionary(g => g.Key, g => g);
var result =
from s in byPrefix['S']
from r in byPrefix['R']
select new { s, r };
正如 Pranav 和 huseyin 所提到的,您只需要拆分成两个列表,然后使用嵌套的foreach
来遍历它们。
var startingList = new List<string> { "S1", "R1", "R2", "S2", "S3" };
List<Tuple<string, string>> result = new List<Tuple<string, string>>();
foreach(var s in startingList.Where(x => x.StartsWith("S")).ToList())
{
foreach(var r in startingList.Where(x => x.StartsWith("R")).ToList())
{
result.Add(new Tuple<string, string>(s, r));
}
}
如果这总是静态的,我的意思是总是两个列表(或前缀),你可以做嵌套循环:
List<string> list = new List<string>();
list.Add("S1");
list.Add("R1");
list.Add("R2");
list.Add("S2");
list.Add("S3");
环形
foreach (var s in list.Where(l => l.StartsWith("S")))
{
foreach (var r in list.Where(l => l.StartsWith("R")))
{
Console.WriteLine(string.Format("{0} => {1}", s, r));
}
}
或者:
list.Where(l => l.StartsWith("S"))
.ToList()
.ForEach(s => list.Where(l => l.StartsWith("R"))
.ToList()
.ForEach(r => Console.WriteLine(string.Format("{0} => {1}", s, r)))
);
您可以将结果添加到另一个列表,而不是Console.WriteLine
。
这就是我想出的,数组和枚举器的混合:
using System;
using System.Collections.Generic;
using System.Linq;
namespace ConsoleApplication2
{
class Program
{
static void Main(string[] args)
{
var input = new string[] {
"S1",
"R1",
"R2",
"S2",
"S3"
};
foreach (var item in CombinationsOfSAndR(input))
{
Console.WriteLine("{0} -> {1}", item.Key, item.Value);
}
/* OUT:
S1 -> R1
S1 -> R2
S2 -> R1
S2 -> R2
S3 -> R1
S3 -> R2 */
}
static IEnumerable<KeyValuePair<string, string>> CombinationsOfSAndR(string[] input)
{
for (int i = 0; i < input.Length; i++)
{
if (input[i].StartsWith("S"))
{
for (int j = 0; j < input.Length; j++)
{
if (input[j].StartsWith("R"))
{
yield return new KeyValuePair<string, string>(input[i], input[j]);
}
}
}
}
}
}
}
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