LINQ Group依靠伯爵

Question

我正在学习C＃中的LINQ。我有以下JSON数据：

std::string

我想通过对产品进行分组来执行LINQ 然后通过降序排序，最后选择前三名。

我该怎么做？在结果中，我必须显示产品及其数量如下：

[
    {
        "product": [
                   "a", "b", "c"
                  ]
    },
    {
        "product": [
                  "a","b"
                  ]
    },
    {
        "product": [
                   "b","c"
                 ]
    },
    {
       "product": [
                   "b", "c"
                ]
    },
    {
        "product": [
                  "a","b"
                  ]
    },
    {
       "product": [
                   "b", "c"
                ]
    },
    {
        "product": [
                  "a"
                  ]
    },
]

我目前的代码是：

 "b","c"            3
 "a","b"            2 
 "a","b","c"        1

但我得到全部1作为计数。你能帮忙纠正一下结果吗？谢谢。

Answer 1

您正尝试按序列分组，但没有自定义比较器。那不行 要获得所需的输出，请尝试执行以下操作：

定义自定义相等比较器：

public class SequenceComparer : IEqualityComparer<string[]>
{
    public bool Equals(string[] x, string[] y)
    {
        if (ReferenceEquals(x, y))
            return true;
        if (x == null || y == null)
            return false;
        return x.SequenceEqual(y);
    }

    public int GetHashCode(string[] obj)
    {
        return obj.Aggregate(42, (c, n) => c ^ n.GetHashCode());
    }
}

将您的json解析为匿名对象

var json = "[\r\n    {\r\n        \"product\": [\r\n                   \"a\", \"b\", \"c\"\r\n                  ]\r\n    },\r\n    {\r\n        \"product\": [\r\n                  \"a\",\"b\"\r\n                  ]\r\n    },\r\n    {\r\n        \"product\": [\r\n                   \"b\",\"c\"\r\n                 ]\r\n    },\r\n    {\r\n       \"product\": [\r\n                   \"b\", \"c\"\r\n                ]\r\n    },\r\n    {\r\n        \"product\": [\r\n                  \"a\",\"b\"\r\n                  ]\r\n    },\r\n    {\r\n       \"product\": [\r\n                   \"b\", \"c\"\r\n                ]\r\n    },\r\n    {\r\n        \"product\": [\r\n                  \"a\"\r\n                  ]\r\n    },\r\n]";

var products = JsonConvert.DeserializeAnonymousType(json,
  new[] {new {product = new string[] { }}});

使用您的自定义相等比较器按产品分组

var result = products.GroupBy(p => p.product, new SequenceComparer())
    .Select(g => new {g.Key, Count = g.Count()})
    .OrderByDescending(x => x.Count)
    .Take(3);

现在你可以看到一个结果：

foreach (var row in result)
    Console.WriteLine($"{string.Join(",", row.Key)} {row.Count}");

将输出

'b,c' 3
'a,b' 2
'a,b,c' 1

直播demo