按我们想要的特定顺序对 DataTable 的行进行排序

Question

假设我有两列的 DataTable

Column1	Column2
abc	jan
def	dec
cba	feb
bdf	nov
aaa	dec

我有第 2 列的月份列表。 我想按月份排序

输出：

Column1	Column2
def	dec
aaa	dec
bdf	nov
cba	feb
abc	jan

我尝试了什么：

string[] monthList = { "dec", "nov", "oct", "sep",,,, "feb", "jan"};
DataTable dataExistingTable
DataTable temp = new DataTable();
foreach(string month in monthList)
{
  var filteredData = dataExistingTable.AsEnumerable().Where(x => x["Column2"] == month);
  temp.Merge(filteredData.CopyToDataTable());
}

请建议一些更快/更好的方法！！！

Answer 1

Waqas Raja 的回答帮助我解决了问题并写下了这个答案。

按您想要的顺序排序的更简单/更快的方法是使用 DataColumn 的 Expression 属性。

您可以通过多种方式将表达式分配给列

table.Columns.Add(columnName, type, expression);

或

table.Columns.Add(columnName, type);
table.Columns[columnName].Expression = expression;

对于这个问题，我在表达式中使用了 IIF，其作用类似于 If Else 语句
用法：IIF(condition, 'true statement', 'false statement')

想知道什么样的条件可以使用https://docs.microsoft.com/en-us/dotnet/api/system.data.datacolumn.expression?view=net-5.0

下面的方法给出了具有任意数量对象的列表的表达式

  private static string GetColumnExpression(List<object> distinctList, string columnName)
  {
         int counter = 1;
         string expression = "";
         foreach (var item in distinctList)
         {
             expression += $"IIF ([{columnName}] = '{item}', {counter++}, ";
         }
         expression += "0";
         for (int k = 0; k < distinctList.Count; k++)
         {
             expression += ")";
         }

         return expression;
   }

当您应用条件（如 IIF）超过 90/96 的表达式时，它可能会抛出异常，提示 “表达式太复杂”

对于对象超过 90/96 的列表，下面的代码会有所帮助！

private static List<string> GetColumnExpressions(List<string> distinctList, string columnName, string sortingColumn)
            {
                var list = distinctList;
                List<string> expressions = new List<string>();
                int maxLimit = 90, listCount = distinctList.Count, counter = 1, loopCount = 1;
                while (listCount != 0)
                {
                    string expression = "";
                    if (loopCount > 1)
                    {
                        expression = $"IIF ([ExtraCol] <> 0, [ExtraCol], ";
                    }
                    int conditionCount = listCount >= maxLimit ? maxLimit : listCount;
                    for (int i = 0; i < conditionCount; i++)
                    {
                        expression += $"IIF ([{columnName}] = '{list[0]}', {counter++}, ";
                        list.RemoveAt(0);
                    }
                    expression += "0";
                    for (int k = 0; k < conditionCount; k++)
                    {
                        expression += ")";
                    }
                    if (loopCount > 1)
                    {
                        expression += ")";
                    }
                    expressions.Add(expression);
                    listCount = list.Count;
                    loopCount++;
                }
                return expressions;
            }

用法如下：

//"MonthNumber" is column Added For Expression/Sorting
                var expressions = GetColumnExpressions(list, "Column2", "MonthNumber");
                table.Columns.Add("MonthNumber", typeof(int));
                string sourceColumn = "MonthNumber", destColumn = "MonthNumber";
                for (int k = 0; k < expressions.Count; k++)
                {
                    if (k > 0)
                    {
                        destColumn = "Extra" + k;
                        table.Columns.Add(destColumn, typeof(int));
                        for (int row = 0; row < table.Rows.Count; row++)
                        {
                            table.Rows[row][destColumn] = table.Rows[row][sourceColumn];
                        }
                        expressions[k] = expressions[k].Replace("ExtraCol", sourceColumn);
                        sourceColumn = destColumn;
                    }
                    string expression = expressions[k];
                    table.Columns[destColumn].Expression = expression;
                }

排序和删除多余的列

  table.DefaultView.Sort = $"{destColumn}";
  for (int k = expressions.Count - 1; k > 0; k--)
  {
      table.Columns.Remove("Extra" + k);
  }
  table.Columns.Remove("MonthNumber");


var sortedTable = table.defaultView.ToTable();

Answer 2

在我的应用程序中，我通常使用此算法按特殊顺序对不同项目进行排序。只有 OrderedListItem 通常是 DB 表，Column2 通常是 OrderedListItem 的外键。这样我就不需要第二个查询了。

public static void Main()
{
    List<OrderedListItem> orderedList=null;
    List<TableItem> tableItems=null;
    
     PrepareData( ref orderedList, ref tableItems);
     
    var query =
            (from ti in tableItems
             join ol in orderedList on ti.Column2 equals ol.Name
             select new
             {
                 Column1 = ti.Column1,
                 Column2 = ti.Column2,
                 OrderNum = ol.OrderNum
             }).OrderBy(i => i.OrderNum)
            .ToArray();

    var result = query.Select(q => new TableItem { Column1 = q.Column1, Column2 = q.Column2 }).ToArray();
    
}

public static void PrepareData(ref List<OrderedListItem> orderedList, ref List<TableItem> tableItems)
{
         orderedList = new List<OrderedListItem> {
            new OrderedListItem ( 1,"Jan",100),
            new OrderedListItem ( 2,"Feb",200),
            new OrderedListItem ( 3,"Mar",300),
            new OrderedListItem  ( 4, "Apr",400)
            };

     tableItems = new List<TableItem> {
     new TableItem  {Column1="cba", Column2="Feb"},
             new TableItem  {Column1="abc", Column2="Jan"},
            
    };
}


public class OrderedListItem
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int OrderNum { get; set; }
    
    public  OrderedListItem(int id, string name, int orderNum)
    {
        
            Id=id;
            Name=name;
            OrderNum=orderNum;
    }
}
public class TableItem
{
        public string Column1 { get; set; }
        public string Column2 { get; set; }
}

Answer 3

添加基于表达式的列

dataExistingTable.Columns.Add("MonthNumber", typeof(int),
    "IIF ([Column2] = 'dec', 12, (IIF ([Column2] = 'nov', 11, (IIF ([Column2] = 'oct', 10, (IIF ([Column2] = 'sep', 9, 8)))))))");

然后对基于表达式的列应用排序

dataExistingTable.DefaultView.Sort = "MonthNumber desc";

然后表格的 DefaultView 会给你排序的行。

// dataExistingTable.DefaultView;