linq

问题 I have a collection like this, Class Base{} Class A : Base {} Class B : Base {} List<Base> collection = new List<Base>(); collection.Add(new A()); collection.Add(new B()); collection.Add(new A()); collection.Add(new A()); collection.Add(new B()); Now I want to sort the collection based on type (A/B). How I can do this? Please help me. 回答1: You can use the type information itself: collection.Sort( (a,b) => { bool aType = a.GetType() == typeof(A); bool bType = b.GetType() == typeof(A); return

问题 I want to GroupBy multiple objects in a list of records and not simply multiple values. I am having trouble getting grouping to work with reference type objects. I have a collection of objects that contain Room, Type, and DateTime. Room, Type, and DateTime all have properties associated with them. I've already added the IEquateable interface to the room and the type thinking that would be enough to with with group by. var groups = collection .Where(g => g.Stage == InventoryStage.StageA)

问题 I have a table that I need to summarize in a report. This is my sample table. Orders _____________________________________ CustomerId | CustomerName | OrderType ___________|______________|__________ 1 | Adam | Shoe 1 | Adam | Shoe 1 | Adam | Shoe 1 | Adam | Hat 1 | Adam | Hat 2 | Bill | Shoe 2 | Bill | Hat 3 | Carl | Sock 3 | Carl | Hat I am trying to summarize this to pass back in my viewmodel without a loop. This is the result that I am attempting to achieve. CustomerName | Shoe | Hat |

问题 I have a code that fetching a table. Here's my sample code: public IQueryable<MyItem> MyItems(){ return context.MyItem; } Here are the sample properties of MyItem public int Id {get;set;} public byte[] Image {get;set;} public string Name {get;set;} Since, byte[] can have multiple characters, I don't want to include then in searching because it will take so long if I have a records like 10,000 items. Typically, I would Select like this: public IQueryable<MyItem> MyItems(){ return context

问题 is it possible to define a LINQ statement for the following problems WITHOUT using a foreach loop? public class GroupObject { public String name; public List<String> letters; public void test() { List<GroupObject> myGroups = new List<GroupObject> { new GroupObject { name="test1", letters=new List<String>{"x","y","z"} }, new GroupObject { name="test2", letters=new List<String>{"l","m","n"} }, new GroupObject { name="test3", letters=new List<String>{"m","x","z"} } }; // LINQ problem 1: how to

问题 I would like a third column "items" with the values that are grouped. var dic = new Dictionary<string, int>(); dic.Add("a", 1); dic.Add("b", 1); dic.Add("c", 2); dic.Add("d", 3); var dCounts = (from i in dic group i by i.Value into g select new { g.Key, count = g.Count()}); var a = dCounts.Where(c => c.count>1 ); dCounts.Dump(); a.Dump(); This code results in: Key Count 1 2 2 1 3 1 I would like these results: Key Count Items 1 2 a, b 2 1 c 3 1 d 回答1: var dCounts = (from i in dic group i by i

问题 I would like a third column "items" with the values that are grouped. var dic = new Dictionary<string, int>(); dic.Add("a", 1); dic.Add("b", 1); dic.Add("c", 2); dic.Add("d", 3); var dCounts = (from i in dic group i by i.Value into g select new { g.Key, count = g.Count()}); var a = dCounts.Where(c => c.count>1 ); dCounts.Dump(); a.Dump(); This code results in: Key Count 1 2 2 1 3 1 I would like these results: Key Count Items 1 2 a, b 2 1 c 3 1 d 回答1: var dCounts = (from i in dic group i by i

问题 I have the code: var predicate = PredicateBuilder.True<Value>(); predicate = predicate.And(x => x.value1 == "1"); predicate = predicate.And(x => x.value2 == "2"); var vals = Value.AsExpandable().Where(predicate).ToList(); If I have PredicateBuilder.True<Value>() , it brings back what I expect, but if I have PredicateBuilder.False<Value>() , it brings back 0 records. Can someone explain what the the difference is and why in one scenario I get back 0 records an in the other I get what I expect.

问题 I have the code: var predicate = PredicateBuilder.True<Value>(); predicate = predicate.And(x => x.value1 == "1"); predicate = predicate.And(x => x.value2 == "2"); var vals = Value.AsExpandable().Where(predicate).ToList(); If I have PredicateBuilder.True<Value>() , it brings back what I expect, but if I have PredicateBuilder.False<Value>() , it brings back 0 records. Can someone explain what the the difference is and why in one scenario I get back 0 records an in the other I get what I expect.

问题 I'm trying to figure out the best way to custom sort a List. Lets say that T is a Object with a date(DateTime?) property and a status(string) property. I have 3 cases... "Urgent": I want these at the top of the list, no particular order date = null status = "Urgent" "Normal": I want these ordered by date after the Urgent cases date = any valid date/time status = "On Time" "Later": I want these at the bottom of the list, no particular order date = null status = "Later" Any thoughts? Should I