Question

我有一个包含具有groupnumber属性的对象的IEnumerable。我希望能够获得具有重复分组编号的所有对象的列表，例如

obj1：groupnumber = 1 KEEP
obj2：groupnumber = 2 DELETE
obj3：groupnumber = 1 KEEP

我可以使用以下内容获取所有重复的组号的列表

   var duplicates = from c in sorted 
                    group c by c.groupnumber into g 
                    where g.Count() > 1 
                    select new { groupnumber = g.Key, recs = g.Count() };

但我无法弄清楚如何清除所有单个实例对象的列表

干杯

Answer 1

这是最简单的选项（我认为）：

sorted.GroupBy( c => c.groupnumber )
      .Where( g => g.Count() > 1 )
      .SelectMany( g => g );

或者，尝试以下方法：

var duplicates = from c in sorted 
                 group c by c.groupnumber into g 
                 where g.Count() > 1
                 select g.Key;

// convert the list to a lookup object for efficiency
var dupLookup = duplicates.ToLookup( c => c );

// exclude all items that are NOT one of the duplicate group keys
var excludeNonDups = sorted.Where( c => !dupLookup.Contains( c ) )

Answer 2

好吧，我必须读几遍你的问题。我的理解是你想“选择集合中有多个obj的所有obj，并且具有相同的groupnumber”...所以过滤掉具有唯一groupnumbers的obj。

如果是这样的话，那你几乎就到了！使用SelectMany将群组折叠为单个群集。

var duplicates = (from c in sorted
    group c by c.groupnumber into g
    where g.Count() > 1
    select g).SelectMany(grp => grp);

Answer 3

如果您只想要其中一个重复项，请添加对Distinct（）的调用：

var duplicates = (from c in sorted 
                  group c by c.groupnumber into g 
                  where g.Count() > 1 
                  select new { groupnumber = g.Key, recs = g.Count() }).Distinct();

保持重复

3 个答案: