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 result = items.OrderBy(x => x.Name)
                  .ThenByDescending(x => x.OddValue)
                  .GroupBy(s => new {s.IdSelectionType, s.Name, s.Visible})
                  .Select(x => x.FirstOrDefault())
                  .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/Union

var originalList = new[]

        {

            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},

        };

        var noneNulls = originalList.Where(ol => ol.OddValue != null);

        var endList = originalList

            .Where(ol => !noneNulls.Select(nn => nn.IdSelectionType).Contains(ol.IdSelectionType))

            .Union(noneNulls);

工作示例：https ://dotnetfiddle.net/UJ8FaS