DEMO:
var listTest = new List<RECORD_DETAIL>();
listTest.Add(new RECORD_DETAIL { SYS_ID = 1, SYS_NO = "A" });
listTest.Add(new RECORD_DETAIL { SYS_ID = 1, SYS_NO = "AA" });
listTest.Add(new RECORD_DETAIL { SYS_ID = 2, SYS_NO = "B" });
var modelsGroup = listTest.GroupBy(x => x.SYS_ID).ToList();
IGrouping<int, RECORD_DETAIL> models = modelsGroup[0];
int groupCount = models.Count<RECORD_DETAIL>();
C# List按某对象的属性分组 IGrouping
原文：https://www.cnblogs.com/johsan/p/12447562.html
