c# - 如何使用 LINQ 获取日期范围内的平均值

Question

我正在尝试确定是否可以在 LINQ to Objects 语句中完成以下操作。

我有一个字典，键为 DateTime(键是多天的值)和一个 double 值。我有太多数据无法绘制在图表上，因此想要每 5 分钟的平均值。

示例输入

01/01/2012 23:53    5
01/01/2012 23:54    2
01/01/2012 23:55    1
01/01/2012 23:56    3
01/01/2012 23:57    4
01/01/2012 23:58    5
01/01/2012 23:59    6
02/01/2012 00:00    2
02/01/2012 00:01    4
02/01/2012 00:02    5

预期输出

01/01/2012 23:55    3
02/01/2012 00:00    4.4

Answer 1

使用这个 helper方法:

static DateTime RoundToNearestInterval(DateTime dt, TimeSpan d)
{
   int f=0;
   double m = (double)(dt.Ticks % d.Ticks) / d.Ticks;
   if (m >= 0.5)
       f=1;            
   return new DateTime(((dt.Ticks/ d.Ticks)+f) * d.Ticks);
}

就这么简单

var result = from kvp in data
             let key = RoundToNearestInterval(kvp.Key, TimeSpan.FromMinutes(5))
             group kvp by key into g
             select new { g.Key, Value = g.Average(x => x.Value) };

或

var result = data.GroupBy(kvp => RoundToNearestInterval(kvp.Key, TimeSpan.FromMinutes(5)), kvp => kvp.Value)
                 .Select(g => new { g.Key, Value = g.Average() });

---

LINQPad 示例:

void Main()
{
    var tmp = new Dictionary<string, int>
    {
        {"01/01/2012 23:53", 5},
        {"01/01/2012 23:54", 2},
        {"01/01/2012 23:55", 1},
        {"01/01/2012 23:56", 3},
        {"01/01/2012 23:57", 4},
        {"01/01/2012 23:58", 5},
        {"01/01/2012 23:59", 6},
        {"02/01/2012 00:00", 2},
        {"02/01/2012 00:01", 4},
        {"02/01/2012 00:02", 5}
    };
    var data = tmp.ToDictionary(d => DateTime.Parse(d.Key), d=>d.Value);

    var result = from kvp in data
                 let key = RoundToNearestInterval(kvp.Key, TimeSpan.FromMinutes(5))
                 group kvp by key into g
                 select new {g.Key, Value = g.Average (x => x.Value) };

    result.ToDictionary(r => r.Key, v => v.Value).Dump();
}