C# 在列表中分组和计数
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Group by and count in List
提问by w00
I have an List which is filled with ints, like this:
我有一个充满整数的列表，如下所示：
[0] 1
[1] 4
[2] 4
[3] 8
[4] 9
[5] 1
[6] 1
So basically random numbers in there, but the same number can occure multiple times in that list.
所以基本上是随机数，但相同的数字可以在该列表中多次出现。
What i want is to group them by number, but that i can also tell how many times that number was in the list. So that i have a something like:
我想要的是按数字对它们进行分组，但我也可以知道该数字在列表中的次数。所以我有一个类似的东西：
[0]
[number] 1
[total] 3 // Occured 3 times in the list
[1]
[number] 4
[total] 2
[2]
[number] 8
[total] 1
[3]
[number] 9
[total] 1
Is there a fast/easy way to accomplish this? Or do i have the write out all sorts of loops and checks to construct something like this manually?
有没有快速/简单的方法来实现这一目标？或者我是否有写出各种循环和检查来手动构造这样的东西？
采纳答案by Tim Schmelter
Use GroupByand Count:
使用GroupBy和Count：
var numberGroups = numbers.GroupBy(i => i);
foreach(var grp in numberGroups)
{
var number = grp.Key;
var total = grp.Count();
}
Here's another example which uses an anonymous type to store some informations. It also creates an array since it seems to be the desired result:
这是另一个使用匿名类型存储一些信息的示例。它还创建一个数组，因为它似乎是所需的结果：
var numberGroups = numbers.GroupBy(i => i)
.Select(grp => new{
number = grp.Key,
total = grp.Count(),
average = grp.Average(),
minimum = grp.Min(),
maximum = grp.Max()
})
.ToArray();
foreach (var numInfo in numberGroups)
{
var number = numInfo.number;
// ...
var maximum = numInfo.maximum;
}
回答by Nikhil Agrawal
Use this
用这个
var result = numbers.GroupBy(n => n)
.Select(c => new { Key = c.Key, total = c.Count() });
回答by Jamie Dixon
Using Tims method from above with a Select rather than a foreach you could do:
将上面的 Tims 方法与 Select 而不是 foreach 一起使用，您可以执行以下操作：
var itemsByGroupWithCount = numbers.GroupBy(i => i)
.Select(item => new {
Number = item.Key,
Total = item.Count()});
回答by Marc
Here's an example of all sorts of loops and checks:
这是各种循环和检查的示例：
var items = new Dictionary<int,int>();
foreach(var number in numbers)
{
if(items.ContainsKey(number))
items[number]++;
else
items.Add(number, 1);
}
Just for reference anyway. I prefer the LINQ approach, but it's not really as bad of a problem as you may have believed.
反正仅供参考。我更喜欢 LINQ 方法，但它并没有您想象的那么严重。
回答by solmon
My solution:
我的解决方案：
var result = from i in n
group i by i into g
select new {g.Key, Count= g.Count()};
回答by pvsfair
Using only the GroupBymethod you could do it like this:
仅使用GroupBy您可以这样做的方法：
var itemsResult = numbers.GroupBy(i => i,
i => i,
(keys, numbersGrouped) =>
new{
number = numbersGrouped.FirstOrDefault(),
total = numbersGrouped.Count()
}
);
It outperforms the GroupBy + Selectmethod proposed by the others executing in less than a half of the time comparing to the other implementations.
GroupBy + Select与其他实现相比，它在不到一半的时间内执行其他人提出的方法。
You can check below the performance comparison:
您可以查看下面的性能比较：
https://dotnetfiddle.net/0M2aKD
https://dotnetfiddle.net/0M2aKD
This is the docsfor the function used if you want to check how does it works
如果您想检查它是如何工作的，这是所用函数的文档
