如何使用“Group by”LINQ？

Question

我使用Linq和DataSet for excel multi sheet。 LINQ如何使用Group？

样本数据：

Name        | Rate | Date       | Code | ROW_SEQ
A           | 12   | 01/01/2015 | 12   | 1
B           | 13   | 01/01/2015 | 12   | 2
Sub Total   | 25   | 01/01/2015 | 12   | 
C           | 10   | 01/01/2015 | 12   | 3
Grand Total | 35   | 01/01/2015 | 12   | 
D           | 15   | 10/01/2015 | 15   | 1
E           | 16   | 10/01/2015 | 15   | 2
Sub Total   | 31   | 10/01/2015 | 15   | 
F           | 10   | 10/01/2015 | 15   | 3
Grand Total | 41   | 10/01/2015 | 15   |

C＃代码：

protected void btnExportExcel_Click(object sender, EventArgs e)
{              
    /*== How to use Group by LINQ? ==*/
    DataSet dsTmp = new DataSet();
    DataTable dtTmp = dtExport.Copy();
    var grouped = from table in dtTmp.AsEnumerable()
        group table by new { date_Col = table["date"] , code_Col = table["code"] } into groupby
        select new
        {
            Value = groupby.Key,
            ColumnValues = groupby
        };
    /*== How to use Group by LINQ? ==*/

    foreach (var key in grouped)
    {
        dtTmp = new DataTable();
        dtTmp = dtExport.Clone();
        dtTmp.TableName = (key.Value.settle_date_Col + "-" + key.Value.bank_code_Col).Replace("00:00:00", "").Replace("/","");
        foreach (var rw in key.ColumnValues)
        {
            dtTmp.ImportRow(rw);
        }
        dtTmp.AcceptChanges();
        dsTmp.Tables.Add(dtTmp.Copy());
    }
    dsTmp.AcceptChanges(); 
    string fileName = string.Format("{0}_{1}.xls", this._ID, DateTime.Now.ToString("yyyyMMdd_HHmmss"));
    ExcelMultiSheet.ToExcel(dsTmp, fileName, Page.Response);          

}

代码结果：

Sheet1
Name        | Rate | Date       | Code | ROW_SEQ
A           | 12   | 01/01/2015 | 12   | 1
B           | 13   | 01/01/2015 | 12   | 2
C           | 10   | 01/01/2015 | 12   | 3

Sheet2
Name        | Rate | Date       | Code | ROW_SEQ
Sub Total   | 25   | 01/01/2015 | 12   |
Grand Total | 35   | 01/01/2015 | 12   |

Sheet3
Name        | Rate | Date       | Code | ROW_SEQ
D           | 15   | 10/01/2015 | 15   | 1
E           | 16   | 10/01/2015 | 15   | 2 
F           | 10   | 10/01/2015 | 15   | 3

Sheet4
Name        | Rate | Date       | Code | ROW_SEQ
Sub Total   | 31   | 10/01/2015 | 15   |
Grand Total | 41   | 10/01/2015 | 15   |

但我需要结果：

Sheet1
    Name        | Rate | Date       | Code | ROW_SEQ
    A           | 12   | 01/01/2015 | 12   | 1
    B           | 13   | 01/01/2015 | 12   | 2
    Sub Total   | 25   | 01/01/2015 | 12   |
    C           | 10   | 01/01/2015 | 12   | 3
    Grand Total | 35   | 01/01/2015 | 12   |

Sheet2
    Name        | Rate | Date       | Code | ROW_SEQ
    D           | 15   | 10/01/2015 | 15   | 1
    E           | 16   | 10/01/2015 | 15   | 2
    Sub Total   | 31   | 10/01/2015 | 15   |
    F           | 10   | 10/01/2015 | 15   | 3
    Grand Total | 41   | 10/01/2015 | 15   |

谢谢你。 :)

Answer 1

你可以像这样使用

var results = from p in persons
              group p.car by p.PersonId into g
              select new { PersonID = g.Key, Cars = g.ToList() };