LINQ to Entities - 在分组数据中创建中值

Question

我有一个 LINQ to Entities 查询用于对数据进行分组并同时添加一些聚合，除了中值计算之外它可以工作。中值是按排好序的列除以 2 计算的（从列中获取中间值）。这是我的例子：

private void button2_Click(object sender, EventArgs e)
    {
        var query = from t in _database.jon_export
                    orderby t.businessEmployeeCount
                    group t by t.county.ToString() into g
                    where g.Count() > 0
                    select new
                    {
                        County = g.Key,
                        CountValue = g.Count(),
                        BusinessEmployeeCount = g.Count(),
                        BusinessEmployeeAverageValue = g.Average(x => x.businessEmployeeCount),
                        //Median value from businessEmployeeCount column
                        BusinessRevenueAverageValue = g.Average(x => x.businessRevenue),  
                        BusinessTurnover=g.Average(x => x.businessTurnover),
                        BooiqEconomicWellBeing=g.Average(x=>x.booiqEconomicWellBeing)
                    };
        this.dataGridView1.DataSource = query.ToList();
    }

Answer 1

在 IEnumerable 上编写扩展方法，并在代码中使用正确的属性调用该扩展方法。

public static double Median(this IEnumerable<int> items)
{
    var data = items.OrderBy(n => n).ToArray();
    if (data.Length % 2 == 0)
        return (data[data.Length / 2 - 1] + data[data.Length / 2]) / 2.0;
    return data[data.Length / 2];
}

后来在上面提到的sn -p中添加如下：

businessEmployeeMedian =  g.Select(x => x.businessEmployeeCount).Median(), 

用于跳过带有 null 的 businessEmployeeCount

businessEmployeeMedian = g.Where(x => x.businessEmployeeCount.HasValue).Select(x => (int)x.businessEmployeeCount).Median()

方法语法中的完整 linq

            var items = _database.jon_export
            .OrderBy(item => item.businessEmployeeCount)
            .GroupBy(item => item.County)
            .Where(g => g.Any())
            .Select(g => {
                return new
                {
                    County = g.Key,
                    CountValue = g.Count(),
                    BusinessEmployeeCount = g.Count(),
                    BusinessEmployeeAverageValue = g.Average(x => x.businessEmployeeCount),
                    businessEmployeeMedian = g.Where(x => x.businessEmployeeCount.HasValue).Select(x => (int)x.businessEmployeeCount).Median(),
                    BusinessRevenueAverageValue = g.Average(x => x.businessRevenue),
                    BusinessTurnover = g.Average(x => x.businessTurnover),
                    BooiqEconomicWellBeing = g.Average(x => x.booiqEconomicWellBeing)
                };
            }).ToList();