[Linq] DataTable에서 Linq 사용하기 Group By

using System;
using System.Linq;
using System.Data;

class Test_Linq
{
	static void Main()
	{
		DataTable table = new DataTable();
		table.Columns.Add("lot");
		table.Columns.Add("data",typeof(double));
		
		table.Rows.Add("A", 45.2);
		table.Rows.Add("A", 45.8);
		table.Rows.Add("A", 45.9);
		table.Rows.Add("B", 45.1);
		table.Rows.Add("B", 45.5);
		
		table.AcceptChanges();
		
		// Group By
		var query = 
			from dr in table.AsEnumerable()
			group dr by dr["lot"] into gg
			select new
			{
				lot = gg.Key,
				count = gg.Count(),
				min = gg.Min(r=>r.Field<double>("data")),
				max = gg.Max(r=>r.Field<double>("data")),
				mean = Math.Round(gg.Average(r=>r.Field<double>("data")), 4),
				sum = gg.Sum(r=>r.Field<double>("data")),
				qsm = gg.Sum(r=>Math.Pow(r.Field<double>("data"), 2))
			};
		
		// Display
		double stdDev = 0;
		Console.WriteLine("**. Select 결과");
		Console.WriteLine("Lot\t개수\t최대값\t최소값\t평균\t합계\t제곱합\t표준편차");
		foreach(var x in query)
		{
			stdDev = Math.Sqrt((x.qsm-x.count*(x.mean*x.mean))/(x.count-1));
			stdDev = Math.Round(stdDev, 4);
			
			Console.WriteLine(
				"{0}\t{1}\t{2}\t{3}\t{4}\t{5}\t{6}\t{7}", 
				x.lot, x.count, x.max, x.min, x.mean, x.sum, x.qsm, stdDev
			);
		}
	}	
}