使用 lambda 对多列进行分组

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最佳答案

var query = source.GroupBy(x => new { x.Column1, x.Column2 });

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如果你的桌子是这样的话

rowId     col1    col2    col3    col4
1          a       e       12       2
2          b       f       42       5
3          a       e       32       2
4          b       f       44       5




var grouped = myTable.AsEnumerable().GroupBy(r=> new {pp1 =  r.Field<int>("col1"), pp2 = r.Field<int>("col2")});

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除了上面的 Aduchis答案-如果你需要根据这些按键组进行过滤，你可以定义一个类来包装许多键。

return customers.GroupBy(a => new CustomerGroupingKey(a.Country, a.Gender))
.Where(a => a.Key.Country == "Ireland" && a.Key.Gender == "M")
.SelectMany(a => a)
.ToList();

CustomerGroupingKey 取组键的位置:

    private class CustomerGroupingKey
{
public CustomerGroupingKey(string country, string gender)
{
Country = country;
Gender = gender;
}


public string Country { get; }


public string Gender { get; }
}

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     class Element
{
public string Company;
public string TypeOfInvestment;
public decimal Worth;
}


class Program
{
static void Main(string[] args)
{
List<Element> elements = new List<Element>()
{
new Element { Company = "JPMORGAN CHASE",TypeOfInvestment = "Stocks", Worth = 96983 },
new Element { Company = "AMER TOWER CORP",TypeOfInvestment = "Securities", Worth = 17141 },
new Element { Company = "ORACLE CORP",TypeOfInvestment = "Assets", Worth = 59372 },
new Element { Company = "PEPSICO INC",TypeOfInvestment = "Assets", Worth = 26516 },
new Element { Company = "PROCTER & GAMBL",TypeOfInvestment = "Stocks", Worth = 387050 },
new Element { Company = "QUASLCOMM INC",TypeOfInvestment = "Bonds", Worth = 196811 },
new Element { Company = "UTD TECHS CORP",TypeOfInvestment = "Bonds", Worth = 257429 },
new Element { Company = "WELLS FARGO-NEW",TypeOfInvestment = "Bank Account", Worth = 106600 },
new Element { Company = "FEDEX CORP",TypeOfInvestment = "Stocks", Worth = 103955 },
new Element { Company = "CVS CAREMARK CP",TypeOfInvestment = "Securities", Worth = 171048 },
};


//Group by on multiple column in LINQ (Query Method)
var query = from e in elements
group e by new{e.TypeOfInvestment,e.Company} into eg
select new {eg.Key.TypeOfInvestment, eg.Key.Company, Points = eg.Sum(rl => rl.Worth)};






foreach (var item in query)
{
Console.WriteLine(item.TypeOfInvestment.PadRight(20) + " " + item.Points.ToString());
}




//Group by on multiple column in LINQ (Lambda Method)
var CompanyDetails =elements.GroupBy(s => new { s.Company, s.TypeOfInvestment})
.Select(g =>
new
{
company = g.Key.Company,
TypeOfInvestment = g.Key.TypeOfInvestment,
Balance = g.Sum(x => Math.Round(Convert.ToDecimal(x.Worth), 2)),
}
);
foreach (var item in CompanyDetails)
{
Console.WriteLine(item.TypeOfInvestment.PadRight(20) + " " + item.Balance.ToString());
}
Console.ReadLine();


}
}

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我想出了一个混合的定义类，比如 David 的答案，但是不需要 Where 类。它看起来像这样:

var resultsGroupings = resultsRecords.GroupBy(r => new { r.IdObj1, r.IdObj2, r.IdObj3})
.Select(r => new ResultGrouping {
IdObj1= r.Key.IdObj1,
IdObj2= r.Key.IdObj2,
IdObj3= r.Key.IdObj3,
Results = r.ToArray(),
Count = r.Count()
});






private class ResultGrouping
{
public short IdObj1{ get; set; }
public short IdObj2{ get; set; }
public int IdObj3{ get; set; }


public ResultCsvImport[] Results { get; set; }
public int Count { get; set; }
}

其中 resultRecords是我正在分组的初始列表，它是 List<ResultCsvImport>。注意，这里的想法是，我将按3列进行分组，即 IdObjec1和 IdObjec2以及 IdObjec3