LINQ GroupBy on count

Question

我正在用 C# 学习 LINQ。我有以下 JSON 数据：

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

我想通过将产品分组到其计数来执行 LINQ然后按降序排序，最后选择前 3 名。

我该怎么做？在结果中，我必须显示产品及其计数，如下所示：

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

我当前的代码是：

public class Product
{
    public List<string> Name { get; set; }
}
string json = File.ReadAllText("products.json");
var products = JsonConvert.DeserializeObject<List<Product>>(json);
var result = (from p in products
              .GroupBy(pt => pt.Name)
              .OrderByDescending(pt => pt.Count())
              .SelectMany(pt => pt) 
              select p).Take(3);

但我得到了所有 1 作为计数。你能帮忙纠正结果吗？谢谢。

Answer 1

您正在尝试按序列分组，但没有自定义比较器。那行不通。
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

json 解析为匿名对象

var json = "[rn    {rn        "product": [rn                   "a", "b", "c"rn                  ]rn    },rn    {rn        "product": [rn                  "a","b"rn                  ]rn    },rn    {rn        "product": [rn                   "b","c"rn                 ]rn    },rn    {rn       "product": [rn                   "b", "c"rn                ]rn    },rn    {rn        "product": [rn                  "a","b"rn                  ]rn    },rn    {rn       "product": [rn                   "b", "c"rn                ]rn    },rn    {rn        "product": [rn                  "a"rn                  ]rn    },rn]";
var products = JsonConvert.DeserializeAnonymousType(json,
  new[] {new {product = new string[] { }}});

使用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);

现在您可以看到一个结果：

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

现场演示