如何使用LINQ按星期几计算各仪表的平均值？

我刚接触C#，首次使用LINQ查询。现有一个类型为Dictionary<(int MeterId, DateTime TimeStamp), float>的字典，数据示例如下：

<(10411, 12/1/2022 12:30:00 AM), 5700>
<(10411, 13/1/2022 12:30:00 AM), 5200>
<(10412, 12/1/2022 12:30:00 AM), 200>

需要编写方法将每个仪表的每周各天平均值存入列表，已写出部分LINQ代码，但不确定如何为AveragedMeter类的各星期平均值属性赋值。

AveragedMeter类定义：

class AveragedMeter
{
    public int MeterId { get; set; }
    public float AverageMondayValue { get; set; }
    public float AverageTuesdayValue { get; set; }
    public float AverageWednesdayValue { get; set; }
    public float AverageThursdayValue { get; set; }
    public float AverageFridayValue { get; set; }
    public float AverageSaturdayValue { get; set; }
    public float AverageSundayValue { get; set; }
}

现有方法代码：

public static List<AveragedMeter> CalculateAverageValues(Dictionary<(int MeterId, DateTime TimeStamp), float> groupedMeterValues)
{
    var lstResult = groupedMeterValues
        .GroupBy(m => new { m.Key.MeterId, m.Key.TimeStamp.DayOfWeek })
        .Select(g => new AveragedMeter
        {
            MeterId = g.Key.MeterId,
            AverageMondayValue,
            AverageTuesdayValue,
            AverageWednesdayValue,
            AverageThursdayValue,
            AverageFridayValue,
            AverageSaturdayValue,
            AverageSundayValue
        })
        .ToList();
    return lstResult;
}

你当前的分组逻辑有误——按仪表ID+星期几分组会得到每个仪表每天的独立分组，无法直接映射到AveragedMeter的7个属性。正确思路是先按MeterId分组，再在每个仪表组内计算各星期几的平均值，最后赋值到对应属性。

完整实现代码如下：

public static List<AveragedMeter> CalculateAverageValues(Dictionary<(int MeterId, DateTime TimeStamp), float> groupedMeterValues)
{
    return groupedMeterValues
        // 第一步：按仪表ID分组，将同一仪表的所有数据归为一组
        .GroupBy(m => m.Key.MeterId)
        .Select(meterGroup => new AveragedMeter
        {
            MeterId = meterGroup.Key,
            // 筛选周一数据并计算平均值，无数据时返回0
            AverageMondayValue = meterGroup
                .Where(item => item.Key.TimeStamp.DayOfWeek == DayOfWeek.Monday)
                .Select(item => item.Value)
                .DefaultIfEmpty(0)
                .Average()
                .ToSingle(),
            // 同理处理周二到周日
            AverageTuesdayValue = meterGroup
                .Where(item => item.Key.TimeStamp.DayOfWeek == DayOfWeek.Tuesday)
                .Select(item => item.Value)
                .DefaultIfEmpty(0)
                .Average()
                .ToSingle(),
            AverageWednesdayValue = meterGroup
                .Where(item => item.Key.TimeStamp.DayOfWeek == DayOfWeek.Wednesday)
                .Select(item => item.Value)
                .DefaultIfEmpty(0)
                .Average()
                .ToSingle(),
            AverageThursdayValue = meterGroup
                .Where(item => item.Key.TimeStamp.DayOfWeek == DayOfWeek.Thursday)
                .Select(item => item.Value)
                .DefaultIfEmpty(0)
                .Average()
                .ToSingle(),
            AverageFridayValue = meterGroup
                .Where(item => item.Key.TimeStamp.DayOfWeek == DayOfWeek.Friday)
                .Select(item => item.Value)
                .DefaultIfEmpty(0)
                .Average()
                .ToSingle(),
            AverageSaturdayValue = meterGroup
                .Where(item => item.Key.TimeStamp.DayOfWeek == DayOfWeek.Saturday)
                .Select(item => item.Value)
                .DefaultIfEmpty(0)
                .Average()
                .ToSingle(),
            AverageSundayValue = meterGroup
                .Where(item => item.Key.TimeStamp.DayOfWeek == DayOfWeek.Sunday)
                .Select(item => item.Value)
                .DefaultIfEmpty(0)
                .Average()
                .ToSingle()
        })
        .ToList();
}

关键说明： #

• 分组调整：先按MeterId分组，确保每个组包含同一仪表的所有时间点数据。
• 平均值处理：
  • 用Where筛选对应星期的数据项
  • DefaultIfEmpty(0)避免空序列导致Average()抛出异常
  • Average()返回double类型，通过ToSingle()转换为float匹配属性类型
• 属性赋值：直接将对应星期的平均值赋值到AveragedMeter的对应属性中。

内容的提问来源于stack exchange，提问作者HARINDA VITHANA