重置計數-如果使用C#lambda運算式的特定列中的值不同

有沒有辦法在選擇后重置計數？這是Fiddle中的示例。

這是我得到的結果，

{groupRowId: 1, monthYear: '2020-08', projectName: 'Project 1'}
{groupRowId: 2, monthYear: '2020-08', projectName: 'Project 2'}
{groupRowId: 3, monthYear: '2020-08', projectName: 'Project 3'}
{groupRowId: 4, monthYear: '2021-08', projectName: 'Project 4'}
{groupRowId: 5, monthYear: '2021-08', projectName: 'Project 5'}
{groupRowId: 6, monthYear: '2021-08', projectName: 'Project 6'}

這是我嘗試過的。

public List<object> GenerateDynamicCalendar(List<ProjectResult> result) {
            int row = 1;
     var queryAug = result.Where(c => c.LiveDate != Convert.ToDateTime("1900-01-01 00:00:00.000") && c.LiveDate.Month == 8)
              .GroupBy(c => new { c.Month, c.Name})
              .Select(g => new DynamicProjectCalendarAug
              {
                  GroupRowId = row  ,
                  MonthYear = g.Key.Month,
                  ProjectName = g.Key.Name,
                  Aug = g.Where(c => c.LiveDate != Convert.ToDateTime("1900-01-01 00:00:00.000") && c.LiveDate.Month == 8).Max(c => c.Name)
              }).ToList();
        
            List<object> query = otherMonthResult.Cast<object>()
                .Concat(queryAug)
            return query;
    }

這就是我想要實作的目標。由于MonthYear值不同，我想將計數重置回 1

{groupRowId: 1, monthYear: '2020-08', projectName: 'Project 1'}
{groupRowId: 2, monthYear: '2020-08', projectName: 'Project 2'}
{groupRowId: 3, monthYear: '2020-08', projectName: 'Project 3'}
{groupRowId: 1, monthYear: '2021-08', projectName: 'Project 4'}
{groupRowId: 2, monthYear: '2021-08', projectName: 'Project 5'}
{groupRowId: 3, monthYear: '2021-08', projectName: 'Project 6'}

uj5u.com熱心網友回復：

如果您只按月份分組，您可以使用.GroupBy()'s為每個分組項resultSelector創建一個物件。DynamicProjectCalendarAug它resultSelector利用了提供源元素索引的.Select()多載。它如下所示：

var queryAug = result
    //.Where( ... )
    .GroupBy(
        resultItem => resultItem.Month,
        ( _, itemsInMonth ) => itemsInMonth
             .Select(( item, i ) => new DynamicProjectCalendarAug {
                 GroupRowId = i   1,
                 MonthYear = item.Month,
                 ProjectName = item.Name,
                 //Aug = ...
             }))
    .SelectMany(_ => _)
    .ToList();

對于您的類的簡化實作，此示例輸入：

List<ProjectResult> result = new()
{
    new() { Month = "2020-08", Name = "Project 1"},
    new() { Month = "2020-08", Name = "Project 2"},
    new() { Month = "2020-08", Name = "Project 3"},
    new() { Month = "2021-08", Name = "Project 4"},
    new() { Month = "2021-08", Name = "Project 5"},
    new() { Month = "2021-08", Name = "Project 6"}
};

將有以下輸出：

1  |  2020-08  |  Project 1
2  |  2020-08  |  Project 2
3  |  2020-08  |  Project 3
1  |  2021-08  |  Project 4
2  |  2021-08  |  Project 5
3  |  2021-08  |  Project 6

示例小提琴在這里。

uj5u.com熱心網友回復：

創建了一個示例來展示如何解決這個問題。 https://dotnetfiddle.net/b9mnau

uj5u.com熱心網友回復：

有

record WithRowId(int GroupRowId, MyDto MyDto);
record MyDto(int X, string Val);

var list = new []{ 
    new MyDto(X: 1, Val: "a"),
    new MyDto(X: 1, Val: "b"),
    new MyDto(X: 2, Val: "c"),
    new MyDto(X: 2, Val: "d"),
};

您可以通過以下方式添加組行 ID：

var list2 = new List<WithRowId>();
foreach( var group in list.GroupBy( c => c.X ))
{
    int i = 0;
    foreach(var r in group)
    {
        list2.Add(new WithRowId(1   i  , r));
    }
}


// Method 2
var list2B = list
 .GroupBy( c => c.X)
 .SelectMany( g => g.Select((x, i) => new WithRowId(GroupRowId: i 1, MyDto: x)));

Select第二種方法使用提供索引的鮮為人知的變體。

標籤：C＃ 林克 拉姆达

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