从Datatable中选择,按多个带条件的列分组

您可以按此值降序排列组以获得“MaxRow”,在那里您可以找到 ptime :

var newSort = dtFinal.AsEnumerable()
    .GroupBy(row => new
    {
        Substation = row.Field<string>("Substation"),
        ColumnTitle = row.Field<string>("ColumnTitle")
    })
    .Select(g => new
    {
        g.Key.Substation,
        g.Key.ColumnTitle,
        MaxRow = g.OrderByDescending(row => decimal.Parse(row.Field<string>("ValueAmount"))).First()
    })
    .Select(x => new 
    {
        ptime = x.MaxRow.Field<string>("ptime"), // voilà
        x.Substation,
        x.ColumnTitle,
        ValueAmount = decimal.Parse(x.MaxRow.Field<string>("ValueAmount"))
    });

由于使用了查询语法,在本例中,由于 let :

var newSort = from row in dtFinal.AsEnumerable()
  let xRow = new { Row = row, valueAmount = decimal.Parse(row.Field<string>("ValueAmount")) }
  group xRow by new
  {
     Substation = row.Field<string>("Substation"),
     ColumnTitle = row.Field<string>("ColumnTitle")
  } into grp
  let maxRow = grp.OrderByDescending(x => x.valueAmount).First()
  select new
  {
     ptime = maxRow.Row.Field<string>("ptime"),
     grp.Key.Substation,
     grp.Key.ColumnTitle,
     ValueAmount = maxRow.valueAmount
  };

这可以使用以下2个查询来实现:

var dt = from cu in DtFinals
         group cu.ValueAmount by new
            {
                cu.Substation,
                cu.ColumnTitle,
            } into gs
            select new
            {
                Substation = gs.Key.Substation,
                ColumnTitle = gs.Key.ColumnTitle,
                ValueAmount = gs.Max()
            };

var final = from c in DtFinals
            join d in dt on 
            new {c.Substation, c.ColumnTitle,c.ValueAmount} equals 
            new {d.Substation, d.ColumnTitle, d.ValueAmount}
            select new 
            { 
                ptime = c.Ptime, 
                Substation = d.Substation, 
                ColumnTitle = d.ColumnTitle,
                ValueAmount = d.ValueAmount
            };