Selection 類有 4 個屬性：public class Selection{ string IdSelectionType {get; set;} string Name {get; set;} decimal? OddValue {get; set;} bool Visible {get; set;}}示例數據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}, };我想選擇一個列表，如果有另一個相同但具有 OddValue 的元素！= null，則丟棄具有 OddValue = null 的元素。是否有任何 Linq / MoreLinq 運算符可以做類似的事情？Selections.GroupBy(s => new {s.IdSelectionType, s.Name, s.OddValue, s.Visible}) .Select(g => g.First()).ToList();預期的結果是：
2 回答
弒天下
TA貢獻1818條經驗 獲得超8個贊
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();首先對項目排序Name，OddValue然后按分組Name。OddValue != null在帶有 的條目之前，您將擁有帶有的條目OddValue == null。然后取每個分組的第一個條目。
這也將返回OddValue == null具有相同的條目，而沒有其他條目Name。
最終結果：https ://dotnetfiddle.net/jZ5gs2
MMMHUHU
TA貢獻1834條經驗 獲得超8個贊
你可以使用聯合。選擇所有不具有 OddValue == null 的元素，然后將剩余的（具有 null 的元素）與第一個列表合并。
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
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