Linq GroupBy 并取不为空的条目

Question

Selection 类有 4 个属性：

public class Selection

{

    string IdSelectionType {get; set;}

    string Name {get; set;}

    decimal? OddValue {get; set;}

    bool Visible {get; set;}

}

示例数据

var originalList = new List<Selection>()

        {

            new Selection() {IdSelectionType = "1", Name = "Under (75.50)", Visible = true},

            new Selection() {IdSelectionType = "2", Name = "Under (75.50)", Visible = true},

            new Selection() {IdSelectionType = "1", Name = "Under (75.50)", OddValue = 1.840m, Visible = true},

            new Selection() {IdSelectionType = "2", Name = "Under (75.50)", OddValue = 1.860m, Visible = true},

        };

我想选择一个列表，如果有另一个相同但具有 OddValue 的元素！= null，则丢弃具有 OddValue = null 的元素。

是否有任何 Linq / MoreLinq 运算符可以做类似的事情？

Selections.GroupBy(s =>

          new {s.IdSelectionType, s.Name, s.OddValue, s.Visible})

          .Select(g => g.First()).ToList();

预期的结果是：

Answer 1

var&nbsp;result&nbsp;=&nbsp;items.OrderBy(x&nbsp;=>&nbsp;x.Name) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;.ThenByDescending(x&nbsp;=>&nbsp;x.OddValue) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;.GroupBy(s&nbsp;=>&nbsp;new&nbsp;{s.IdSelectionType,&nbsp;s.Name,&nbsp;s.Visible}) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;.Select(x&nbsp;=>&nbsp;x.FirstOrDefault()) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;.ToList();首先对项目排序Name，OddValue然后按分组Name。OddValue != null在带有 的条目之前，您将拥有带有的条目OddValue == null。然后取每个分组的第一个条目。这也将返回OddValue == null具有相同的条目，而没有其他条目Name。最终结果：https ://dotnetfiddle.net/jZ5gs2

Answer 2

你可以使用联合。选择所有不具有 OddValue == null 的元素，然后将剩余的（具有 null 的元素）与第一个列表合并。https://linqsamples.com/linq-to-objects/set/Unionvar originalList = new[]&nbsp; &nbsp; &nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; new Selection() {IdSelectionType = "1", Name = "Under (75.50)", Visible = true},&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; new Selection() {IdSelectionType = "2", Name = "Under (75.50)", Visible = true},&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //new Selection() {IdSelectionType = "1", Name = "Under (75.50)", OddValue = 1.840m, Visible = true},&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; new Selection() {IdSelectionType = "2", Name = "Under (75.50)", OddValue = 1.860m, Visible = true},&nbsp; &nbsp; &nbsp; &nbsp; };&nbsp; &nbsp; &nbsp; &nbsp; var noneNulls = originalList.Where(ol => ol.OddValue != null);&nbsp; &nbsp; &nbsp; &nbsp; var endList = originalList&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .Where(ol => !noneNulls.Select(nn => nn.IdSelectionType).Contains(ol.IdSelectionType))&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .Union(noneNulls);工作示例：https ://dotnetfiddle.net/UJ8FaS