[英]Select Max value from sublist with LINQ
如何編寫LINQ查詢,該查詢將返回“值”類型的行,其中包含“最大日期”和該日期的“最大值”。 它應該是name =“ Correct”的行
我在最后寫了一個查詢,它可以正常工作,只是試圖找到一種正確的方法。
提前致謝
public class MeasurePoint
{
public int No { get; set; }
public string Weight { get; set; }
public List<Values> Vals { get; set; }
}
public class Values
{
public string Name { get; set; }
public int Val { get; set; }
public DateTime Date { get; set; }
}
public static class Test
{
public static void Calc()
{
var mps = new List<MeasurePoint>();
mps.Add(new MeasurePoint()
{
No = 1,
Vals = new List<Values>()
{
new Values(){Date = DateTime.Now.Date.AddDays(1), Name = "testas", Val = 1},
new Values(){Date = DateTime.Now.Date.AddDays(2), Name = "testas", Val = 5},
new Values(){Date = DateTime.Now.Date, Name = "testas", Val = 15}
}});
mps.Add(new MeasurePoint()
{
No = 2,
Vals = new List<Values>()
{
new Values(){Date = DateTime.Now.Date, Name = "testas", Val = 11},
new Values(){Date = DateTime.Now.Date.AddDays(2), Name = "Correct", Val = 55},
new Values(){Date = DateTime.Now.Date, Name = "testas", Val = 15}
}
});
mps.Add(new MeasurePoint()
{
No = 3,
Vals = new List<Values>()
{
new Values(){Date = DateTime.Now.Date.AddDays(1), Name = "testas", Val = 111},
new Values(){Date = DateTime.Now.Date.AddDays(2), Name = "testas", Val = 52},
new Values(){Date = DateTime.Now.Date, Name = "testas", Val = 15}
}
});
mps.Add(new MeasurePoint()
{
No = 4,
Vals = new List<Values>()
});
var x = mps.ElementAt(0).Vals.Union(mps.ElementAt(1).Vals).Union(mps.ElementAt(2).Vals);
var z = x.Where(p => p.Date == x.Max(d => d.Date)).MaxBy(t=>t.Val);
//One more way I've found
var ttt = mps.SelectMany(p => p.Vals).GroupBy(t=>t.Date).MaxBy(r=>r.Key).MaxBy(g=>g.Val);
}
var max = mps.SelectMany(x => x.Vals)
.Aggregate((a, x) => (x.Date > a.Date) ||
((x.Date == a.Date) && (x.Val > a.Val)) ? x : a);
嘗試這個
var result = mps.Where(m => m.Vals.Count > 0)
.SelectMany(m => m.Vals
.OrderByDescending(v => v.Date)
.Take(1), (m, v) => new {m.No, v.Date, v.Name, v.Val});
編輯 -這是一個新版本,因為問題已變得更加明確
var result = mps.Where(m => m.Vals.Count > 0)
.SelectMany(m => m.Vals)
.OrderByDescending(v => v.Date)
.ThenByDescending(v => v.Val).Take(1);
如果它是IObservable<T>
的方法,同時GroupBy()
返回IEnumerable<T>
如何使用調用MaxBy()
呢?
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