如何使用Linq从对象列表中按月份分组获取最大与最小计数

步骤说明 #

1. 按Month分组并统计数量：利用Linq的GroupBy方法按Month字段分组，通过Count()统计每组元素数量，最终转为字典存储月份与对应计数的映射关系。
2. 获取最大/最小计数及对应月份：从字典的Values集合中调用Max()和Min()得到最大、最小计数，再反向查找对应的月份。

完整代码实现 #

using System;
using System.Collections.Generic;
using System.Linq;

public class Test
{
    public string Month { get; set; }
    public string ID { get; set; }
    public string SubMonth { get; set; }
}

class Program
{
    static void Main()
    {
        List<Test> test = new List<Test>();

        test.Add(new Test { Month = "Sep", ID = "1", SubMonth = "Sep2" });
        test.Add(new Test { Month = "Sep", ID = "1", SubMonth = "Sep3" });
        test.Add(new Test { Month = "Sep", ID = "1", SubMonth = "Sep4" });
        test.Add(new Test { Month = "Sep", ID = "1", SubMonth = "Sep5" });
        test.Add(new Test { Month = "Sep", ID = "1", SubMonth = "Sep6" });

        test.Add(new Test { Month = "Jun", ID = "3", SubMonth = "Jun2" });

        test.Add(new Test { Month = "Jul", ID = "4", SubMonth = "Jul2" });
        test.Add(new Test { Month = "Jul", ID = "4", SubMonth = "Jul3" });

        test.Add(new Test { Month = "Jan", ID = "5", SubMonth = "Jan2" });
        test.Add(new Test { Month = "Jan", ID = "5", SubMonth = "Jan3" });
        test.Add(new Test { Month = "Jan", ID = "5", SubMonth = "Jan4" });
        test.Add(new Test { Month = "Jan", ID = "5", SubMonth = "Jan5" });

        // 分组统计每个月份的元素数量
        var monthCountMap = test.GroupBy(t => t.Month)
                                .ToDictionary(group => group.Key, group => group.Count());

        // 获取最大计数及对应月份
        int maxCount = monthCountMap.Values.Max();
        string maxMonth = monthCountMap.First(kv => kv.Value == maxCount).Key;

        // 获取最小计数及对应月份
        int minCount = monthCountMap.Values.Min();
        string minMonth = monthCountMap.First(kv => kv.Value == minCount).Key;

        // 输出结果
        Console.WriteLine($"最大计数：{maxMonth}月，共{maxCount}个元素");
        Console.WriteLine($"最小计数：{minMonth}月，共{minCount}个元素");
    }
}

输出结果 #

最大计数：Sep月，共5个元素
最小计数：Jun月，共1个元素

内容的提问来源于stack exchange，提问作者Raj