I have a list of errors defined as the following:
List<Errors> test1 = new List<Errors>();
public class Errors
{
public int ID {get; set;}
public int Occurrence {get; set;}
//.....
//.....
}
The errors are unique by the combination of the two fields above.
A second list keeps track of whose been assigned to the errors.
List<Tasks> test2 = new List<Tasks>();
public class Tasks
{
public int ID {get; set;}
public int Occurrence {get; set;}
public int EmployeeID {get; set;}
//.....
}
Also made unique by the same two fields. Essentially the tasks are a subset of the errors that have been assigned to someone.
I would like to use a LINQ query (or equivalent) to determine if the composite ID from the List<Errors> exists in List<Tasks>... To be clear it must use both IDS.
I have found the below solution but have not been able to adopt it to a composite key.
`var test2NotInTest1 = test2.Where(t2 => !test1.Any(t1 => t2.Contains(t1)));`
Just need to use and && operator and check both properties instead of one:
var test2NotInTest1 = test2.Where(t2 => !test1.Any(t1 => t1.ID == t2.ID && t1.Occurance == t2.Occurance);
There is a function for that... Except
var test2NotInTest1 = test1.Except(test2);
If you don't have it you will need to create the interface for equal -- something like this:
var test2NotInTest1 = test1.Except(test2, new ErrorsComparer());
class ErrorsComparer : IEqualityComparer<Errors>
{
public bool Equals(Errors x, Errors y)
{
//Check whether the compared objects reference the same data.
if (Object.ReferenceEquals(x, y)) return true;
//Check whether any of the compared objects is null.
if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
return false;
//Check whether the products' properties are equal.
return x.ID == y.ID && x.Occurrence == y.Occurrence;
}
// If Equals() returns true for a pair of objects
// then GetHashCode() must return the same value for these objects.
public int GetHashCode(Errors e)
{
if (Object.ReferenceEquals(e, null)) return 0;
int hashID = e.ID == null ? 0 : e.ID.GetHashCode();
int hashO = e.Occurrence.GetHashCode();
//Calculate the hash code for the product.
return hashID ^ hashO;
}
}
You were almost there, just add a correct condition to the LINQ expression:
var test2NotInTest1 = listOfErrors.Where(e => !listOfTasks.Any(t => t.ID == e.Id && t.Occurrence == e.Occurrence)).ToList();
For: to determine if the composite ID from the Errors exists in Tasks...
Another approach is to use Enumerable.Join Method
var assignedErrors =
errors.Join(tasks,
error => new { Id = error.Id, Occurrence = error.Occurrence },
task => new { Id = task.Id, Occurrence = task.Occurrence },
(error, task) => error);
For: to determine if the composite ID from the Errors not exists in Tasks..., as in your sample:
var test2NotInTest1 = test2.Where(t2 => !test1.Any(t1 => t2.Contains(t1)));
You can use HashSet to "speed up" search for already assigned errors.
var assignedErrors = tasks.Select(task => (task.Id, task.Occurrence)).ToHashSet();
var notAssignedErrors =
errors.Where(error => assignedErrors.Contains((error.Id, error.Occurrence)) == false)
.ToList();
Or create your own domain specific extension method:
public static IEnumerable<Errors> NotAssignedIn(
this IEnumerable<Errors> errors,
IEnumerable<Tasks> tasks)
{
var assigned = new HashSet<(int Id, int Occurrence)>();
foreach (var task in tasks)
{
assigned.Add((task.Id, task.Occurrence));
}
foreach (var error in errors)
{
if (assigned.Contains((error.Id, error.Occurrence)) == false)
{
yield return error;
}
}
}
Usage:
var notAssignedErrors = errors.NotAssignedIn(tasks);
I'm trying to construct an expression that ultimately results in a query like
SELECT p.*
FROM MyEntity p
WHERE EXISTS(SELECT *
FROM filters
WHERE (filter.type = 1
AND filter.objectid = p.id
AND filter.value = 1
OR filter.type = 1
AND filter.objectid = p.id
AND filter.value = 2))
AND EXISTS(...)
Obviously it won't look exactly like that, but that's the general idea.
I'm using PredicateBuilder to build the query based on the filters passed in, so I have something like this:
var query = context.Set<MyEntity>().AsExpandable();
var predicate = PredicateBuilder.New<MyEntity>(true);
//loop through the group filters. The filters in a group have an or relationship
foreach (FilterGroup group in filters)
{
predicate = predicate.And(
p => context.Set<FilteringValue>().AsExpandable().Any(getFilteringPredicate(p,group ))
);
}
return query.Where(predicate);
And the getFilteringPredicateMethod:
Expression<Func<FilteringValue,bool>> getFilteringPredicate(MyEntity p, FilterGroup filters) {
var fPredicate = PredicateBuilder.New<FilteringValue>(true);
foreach(var filter in filters.FilterList)
{
fPredicate= fPredicate.Or(fv => fv.objectid == p.Id && fv.Type== 1 && fv.value == filter.Value);
}
return fPredicate
}
This seems relatively simple, however I'm getting the error
variable 'p' of type 'Models.MyEntity' referenced from scope '', but it is not defined.
Is there no way to pass the product object into the getFilteringPredicate() method? MyEntity and Filter are not related in Entity Framework.
So... I think I finally got it, you want to relate two expression parameters and build up a composite query (what I mean by the informal definition of "composite" is a subquery having a reference to the main query parameter(s)):
Unfortunately, LinqKit does not support multi-parameter expressions 'AFAIK', which is something that would be a perfect match for your case:
Well, anyway... here it goes. By the way FilteringValues and MyEntities are just two DbSets, I just happen to be using LinqPad to test this out ATM (Questions?):
void Main(string[] args)
{
var entityQuery = MyEntities.AsExpandable();
var filterGroups = GetFilterGroups();
// Initialize with TRUE since no group filter implies Everything matches
var predicate = PredicateBuilder.New<MyEntity>(true);
var filteringValueQuery = FilteringValues.AsExpandable();
foreach (var g in filterGroups)
{
if (!g.FilterList.Any())
{
// If we have no filters in the group, skip
continue;
}
var expressionForGroupFilters = BuildExpressionForGroupFilters(g.FilterList);
predicate = predicate.And(entity => filteringValueQuery.Any(filteringValue => expressionForGroupFilters.Invoke(entity, filteringValue)));
}
entityQuery = entityQuery.Where(predicate);
var data = entityQuery.ToList();
data.Dump();
}
public static Expression<Func<MyEntity, FilteringValue, bool>> BuildExpressionForSingleFilter(Filter groupFilter)
{
var value = groupFilter.Value;
return (entity, filteringValue) =>
filteringValue.Type == 1
&& filteringValue.ObjectId == entity.Id
&& filteringValue.Value == value;
}
public static Expression<Func<MyEntity, FilteringValue, bool>> BuildExpressionForGroupFilters(IReadOnlyCollection<Filter> groupFilters)
{
Expression<Func<MyEntity, FilteringValue, bool>> result = null;
foreach (var groupFilter in groupFilters)
{
var expression = BuildExpressionForSingleFilter(groupFilter);
if (result == null)
{
result = expression;
continue;
}
var tempResult = result.Expand();
result = (entity, filteringValue) => tempResult.Invoke(entity, filteringValue) || expression.Invoke(entity, filteringValue);
}
return result.Expand();
}
public static FilterGroup CreateFilterGroupWithValues(params int[] values)
{
var filterList = values
.Select(x => new Filter { Value = x })
.ToList();
return new FilterGroup { FilterList = filterList };
}
public static IEnumerable<FilterGroup> GetFilterGroups()
{
return new[] {CreateFilterGroupWithValues(0, 2, 4), CreateFilterGroupWithValues(1)};
}
public class Filter
{
public int Value { get; set; }
}
public class FilterGroup
{
public FilterGroup()
{
FilterList = new List<Filter>();
}
public List<Filter> FilterList { get; set; }
}
I have a class called Order which has properties such as OrderId, OrderDate, Quantity, and Total. I have a list of this Order class:
List<Order> objListOrder = new List<Order>();
GetOrderList(objListOrder); // fill list of orders
I want to sort the list based on one property of the Order object; for example, either by the order date or the order id.
How can I do this in C#?
The easiest way I can think of is to use Linq:
List<Order> SortedList = objListOrder.OrderBy(o=>o.OrderDate).ToList();
If you need to sort the list in-place then you can use the Sort method, passing a Comparison<T> delegate:
objListOrder.Sort((x, y) => x.OrderDate.CompareTo(y.OrderDate));
If you prefer to create a new, sorted sequence rather than sort in-place then you can use LINQ's OrderBy method, as mentioned in the other answers.
To do this without LINQ on .Net2.0:
List<Order> objListOrder = GetOrderList();
objListOrder.Sort(
delegate(Order p1, Order p2)
{
return p1.OrderDate.CompareTo(p2.OrderDate);
}
);
If you're on .Net3.0, then LukeH's answer is what you're after.
To sort on multiple properties, you can still do it within a delegate. For example:
orderList.Sort(
delegate(Order p1, Order p2)
{
int compareDate = p1.Date.CompareTo(p2.Date);
if (compareDate == 0)
{
return p2.OrderID.CompareTo(p1.OrderID);
}
return compareDate;
}
);
This would give you ascending dates with descending orderIds.
However, I wouldn't recommend sticking delegates as it will mean lots of places without code re-use. You should implement an IComparer and just pass that through to your Sort method. See here.
public class MyOrderingClass : IComparer<Order>
{
public int Compare(Order x, Order y)
{
int compareDate = x.Date.CompareTo(y.Date);
if (compareDate == 0)
{
return x.OrderID.CompareTo(y.OrderID);
}
return compareDate;
}
}
And then to use this IComparer class, just instantiate it and pass it to your Sort method:
IComparer<Order> comparer = new MyOrderingClass();
orderList.Sort(comparer);
Simplest way to order a list is to use OrderBy
List<Order> objListOrder =
source.OrderBy(order => order.OrderDate).ToList();
If you want to order by multiple columns like following SQL Query.
ORDER BY OrderDate, OrderId
To achieve this you can use ThenBy like following.
List<Order> objListOrder =
source.OrderBy(order => order.OrderDate).ThenBy(order => order.OrderId).ToList();
Doing it without Linq as you said:
public class Order : IComparable
{
public DateTime OrderDate { get; set; }
public int OrderId { get; set; }
public int CompareTo(object obj)
{
Order orderToCompare = obj as Order;
if (orderToCompare.OrderDate < OrderDate || orderToCompare.OrderId < OrderId)
{
return 1;
}
if (orderToCompare.OrderDate > OrderDate || orderToCompare.OrderId > OrderId)
{
return -1;
}
// The orders are equivalent.
return 0;
}
}
Then just call .sort() on your list of Orders
A Classical Object Oriented Solution
First I must genuflect to the awesomeness of LINQ.... Now that we've got that out of the way
A variation on JimmyHoffa answer. With generics the CompareTo parameter becomes type safe.
public class Order : IComparable<Order> {
public int CompareTo( Order that ) {
if ( that == null ) return 1;
if ( this.OrderDate > that.OrderDate) return 1;
if ( this.OrderDate < that.OrderDate) return -1;
return 0;
}
}
// in the client code
// assume myOrders is a populated List<Order>
myOrders.Sort();
This default sortability is re-usable of course. That is each client does not have to redundantly re-write the sorting logic. Swapping the "1" and "-1" (or the logic operators, your choice) reverses the sort order.
// Totally generic sorting for use with a gridview
public List<T> Sort_List<T>(string sortDirection, string sortExpression, List<T> data)
{
List<T> data_sorted = new List<T>();
if (sortDirection == "Ascending")
{
data_sorted = (from n in data
orderby GetDynamicSortProperty(n, sortExpression) ascending
select n).ToList();
}
else if (sortDirection == "Descending")
{
data_sorted = (from n in data
orderby GetDynamicSortProperty(n, sortExpression) descending
select n).ToList();
}
return data_sorted;
}
public object GetDynamicSortProperty(object item, string propName)
{
//Use reflection to get order type
return item.GetType().GetProperty(propName).GetValue(item, null);
}
Using LINQ
objListOrder = GetOrderList()
.OrderBy(o => o.OrderDate)
.ToList();
objListOrder = GetOrderList()
.OrderBy(o => o.OrderId)
.ToList();
Here is a generic LINQ extension method that does not create an extra copy of the list:
public static void Sort<T,U>(this List<T> list, Func<T, U> expression)
where U : IComparable<U>
{
list.Sort((x, y) => expression.Invoke(x).CompareTo(expression.Invoke(y)));
}
To use it:
myList.Sort(x=> x.myProperty);
I recently built this additional one which accepts an ICompare<U>, so that you can customize the comparison. This came in handy when I needed to do a Natural string sort:
public static void Sort<T, U>(this List<T> list, Func<T, U> expression, IComparer<U> comparer)
where U : IComparable<U>
{
list.Sort((x, y) => comparer.Compare(expression.Invoke(x), expression.Invoke(y)));
}
Please let me complete the answer by #LukeH with some sample code, as I have tested it I believe it may be useful for some:
public class Order
{
public string OrderId { get; set; }
public DateTime OrderDate { get; set; }
public int Quantity { get; set; }
public int Total { get; set; }
public Order(string orderId, DateTime orderDate, int quantity, int total)
{
OrderId = orderId;
OrderDate = orderDate;
Quantity = quantity;
Total = total;
}
}
public void SampleDataAndTest()
{
List<Order> objListOrder = new List<Order>();
objListOrder.Add(new Order("tu me paulo ", Convert.ToDateTime("01/06/2016"), 1, 44));
objListOrder.Add(new Order("ante laudabas", Convert.ToDateTime("02/05/2016"), 2, 55));
objListOrder.Add(new Order("ad ordinem ", Convert.ToDateTime("03/04/2016"), 5, 66));
objListOrder.Add(new Order("collocationem ", Convert.ToDateTime("04/03/2016"), 9, 77));
objListOrder.Add(new Order("que rerum ac ", Convert.ToDateTime("05/02/2016"), 10, 65));
objListOrder.Add(new Order("locorum ; cuius", Convert.ToDateTime("06/01/2016"), 1, 343));
Console.WriteLine("Sort the list by date ascending:");
objListOrder.Sort((x, y) => x.OrderDate.CompareTo(y.OrderDate));
foreach (Order o in objListOrder)
Console.WriteLine("OrderId = " + o.OrderId + " OrderDate = " + o.OrderDate.ToString() + " Quantity = " + o.Quantity + " Total = " + o.Total);
Console.WriteLine("Sort the list by date descending:");
objListOrder.Sort((x, y) => y.OrderDate.CompareTo(x.OrderDate));
foreach (Order o in objListOrder)
Console.WriteLine("OrderId = " + o.OrderId + " OrderDate = " + o.OrderDate.ToString() + " Quantity = " + o.Quantity + " Total = " + o.Total);
Console.WriteLine("Sort the list by OrderId ascending:");
objListOrder.Sort((x, y) => x.OrderId.CompareTo(y.OrderId));
foreach (Order o in objListOrder)
Console.WriteLine("OrderId = " + o.OrderId + " OrderDate = " + o.OrderDate.ToString() + " Quantity = " + o.Quantity + " Total = " + o.Total);
//etc ...
}
Anybody working with nullable types, Value is required to use CompareTo.
objListOrder.Sort((x, y) => x.YourNullableType.Value.CompareTo(y.YourNullableType.Value));
//Get data from database, then sort list by staff name:
List<StaffMember> staffList = staffHandler.GetStaffMembers();
var sortedList = from staffmember in staffList
orderby staffmember.Name ascending
select staffmember;
An improved of Roger's version.
The problem with GetDynamicSortProperty is that only get the property names but what happen if in the GridView we use NavigationProperties? it will send an exception, since it finds null.
Example:
"Employee.Company.Name; " will crash... since allows only "Name" as a parameter to get its value.
Here's an improved version that allows us to sort by Navigation Properties.
public object GetDynamicSortProperty(object item, string propName)
{
try
{
string[] prop = propName.Split('.');
//Use reflection to get order type
int i = 0;
while (i < prop.Count())
{
item = item.GetType().GetProperty(prop[i]).GetValue(item, null);
i++;
}
return item;
}
catch (Exception ex)
{
throw ex;
}
}
You can do something more generic about the properties selection yet be specific about the type you're selecting from, in your case 'Order':
write your function as a generic one:
public List<Order> GetOrderList<T>(IEnumerable<Order> orders, Func<Order, T> propertySelector)
{
return (from order in orders
orderby propertySelector(order)
select order).ToList();
}
and then use it like this:
var ordersOrderedByDate = GetOrderList(orders, x => x.OrderDate);
You can be even more generic and define an open type for what you want to order:
public List<T> OrderBy<T,P>(IEnumerable<T> collection, Func<T,P> propertySelector)
{
return (from item in collection
orderby propertySelector(item)
select item).ToList();
}
and use it the same way:
var ordersOrderedByDate = OrderBy(orders, x => x.OrderDate);
Which is a stupid unnecessary complex way of doing a LINQ style 'OrderBy',
But it may give you a clue of how it can be implemented in a generic way
var obj = db.Items.Where...
var orderBYItemId = obj.OrderByDescending(c => Convert.ToInt32(c.ID));
Suppose you have the following code, in this code, we have a Passenger class with a couple of properties that we want to sort based on.
public class Passenger
{
public string Name { get; }
public string LastName { get; }
public string PassportNo { get; }
public string Nationality { get; }
public Passenger(string name, string lastName, string passportNo, string nationality)
{
this.Name = name;
this.LastName = lastName;
this.PassportNo = passportNo;
this.Nationality = nationality;
}
public static int CompareByName(Passenger passenger1, Passenger passenger2)
{
return String.Compare(passenger1.Name, passenger2.Name);
}
public static int CompareByLastName(Passenger passenger1, Passenger passenger2)
{
return String.Compare(passenger1.LastName, passenger2.LastName);
}
public static int CompareNationality(Passenger passenger1, Passenger passenger2)
{
return String.Compare(passenger1.Nationality, passenger2.Nationality);
}
}
public class TestPassengerSort
{
Passenger p1 = new Passenger("Johon", "Floid", "A123456789", "USA");
Passenger p2 = new Passenger("Jo", "Sina", "A987463215", "UAE");
Passenger p3 = new Passenger("Ped", "Zoola", "A987855215", "Italy");
public void SortThem()
{
Passenger[] passengers = new Passenger[] { p1, p2, p3 };
List<Passenger> passengerList = new List<Passenger> { p1, p2, p3 };
Array.Sort(passengers, Passenger.CompareByName);
Array.Sort(passengers, Passenger.CompareByLastName);
Array.Sort(passengers, Passenger.CompareNationality);
passengerList.Sort(Passenger.CompareByName);
passengerList.Sort(Passenger.CompareByLastName);
passengerList.Sort(Passenger.CompareNationality);
}
}
So you can implement your sort structure by using Composition delegate.
I made this extension method for List<T>.
The extension method takes the property you wish to sort as a parsed string and then uses the OrderBy method of the List<T>. Then it sets each index of the original list to the same index of the ordered list.
public static class ListExtensions {
public static void SortBy<T>(this List<T> list, string property, bool reverse = false) {
List<T> ordered = list.OrderBy(obj => obj.GetType().GetProperty(property).GetValue(obj, null)).ToList();
for (int i = 0; i < list.Count; i++)
list[i] = reverse ? ordered[list.Count - 1 - i] : ordered[i];
}
}
If an object in the list has the property Name you sort your list testList as so:
//For normal sorting order
testList.SortBy("Name");
//For reverse sorting order
testList.SortBy("Name", true);
I would recommend that you change the name of SortBy, to something like Prefix_SortBy. To prevent potential collisions if you import another library.
I know this method works for alphabetical and numerical ordering. Its sorting capabilites may be limited yet it is very simple to operate.
If there are some major flaws or issues with this, do tell, I've been programming C# for about 3 months.
Best regards
Make use of LiNQ OrderBy
List<Order> objListOrder=new List<Order> ();
objListOrder=GetOrderList().OrderBy(o=>o.orderid).ToList();
Based on GenericTypeTea's Comparer :
we can obtain more flexibility by adding sorting flags :
public class MyOrderingClass : IComparer<Order> {
public int Compare(Order x, Order y) {
int compareDate = x.Date.CompareTo(y.Date);
if (compareDate == 0) {
int compareOrderId = x.OrderID.CompareTo(y.OrderID);
if (OrderIdDescending) {
compareOrderId = -compareOrderId;
}
return compareOrderId;
}
if (DateDescending) {
compareDate = -compareDate;
}
return compareDate;
}
public bool DateDescending { get; set; }
public bool OrderIdDescending { get; set; }
}
In this scenario, you must instantiate it as MyOrderingClass explicitly( rather then IComparer )
in order to set its sorting properties :
MyOrderingClass comparer = new MyOrderingClass();
comparer.DateDescending = ...;
comparer.OrderIdDescending = ...;
orderList.Sort(comparer);
None of the above answers were generic enough for me so I made this one:
var someUserInputStringValue = "propertyNameOfObject i.e. 'Quantity' or 'Date'";
var SortedData = DataToBeSorted
.OrderBy(m => m.GetType()
.GetProperties()
.First(n =>
n.Name == someUserInputStringValue)
.GetValue(m, null))
.ToList();
Careful on massive data sets though. It's easy code but could get you in trouble if the collection is huge and the object type of the collection has a large number of fields.
Run time is NxM where:
N = # of Elements in collection
M = # of Properties within Object
If you need to sort the Id that is string in Question entity
Use Sort function and delegate to sort the Id after parsing the Id
value
class Question
{
public List<QuestionInfo> Questions Info{ get; set; }
}
class QuestionInfo
{
public string Id{ get; set; }
public string Questions{ get; set; }
}
var questionnaire = new Question();
questionnaire.QuestionInfo.Sort((x, y) => int.Parse(x.Id, CultureInfo.CurrentCulture) - int.Parse(y.Id, CultureInfo.CurrentCulture));
From performance point of view the best is to use a sorted list so that data is sorted as it is added to result.
Other approaches need at least one extra iteration on data and most create a copy of data so not only performance but memory usage will be affected too. Might not be an issue with couple of hundreds of elements but will be with thousands, especially in services where many concurrent requests may do sorting at the same time.
Have a look at System.Collections.Generic namespace and choose a class with sorting instead of List.
And avoid generic implementations using reflection when possible, this can cause performance issues too.
hi just to come back at the question.
If you want to sort the List of this sequence "1" "10" "100" "200" "2" "20" "3" "30" "300" and get the sorted items in this form 1;2;3;10;20;30;100;200;300 you can use this:
public class OrderingAscending : IComparer<String>
{
public int Compare(String x, String y)
{
Int32.TryParse(x, out var xtmp);
Int32.TryParse(y, out var ytmp);
int comparedItem = xtmp.CompareTo(ytmp);
return comparedItem;
}
}
and you can use it in code behind in this form:
IComparer<String> comparerHandle = new OrderingAscending();
yourList.Sort(comparerHandle);
Firstly I have seen IEqualityComparer for anonymous type and the answers there do not answer my question, for the obvious reason that I need an IEqualityComparer not and IComparer for use with Linq's Distinct() method. I have checked the other answers too and these fall short of a solution...
The Problem
I have some code to manipulate and pull records in from a DataTable
var glext = m_dtGLExt.AsEnumerable();
var cflist =
(from c in glext
orderby c.Field<string>(m_strpcCCType),
c.Field<string>(m_strpcCC),
c.Field<string>(m_strpcCCDesc),
c.Field<string>(m_strpcCostItem)
select new
{
CCType = c.Field<string>(m_strpcCCType),
CC = c.Field<string>(m_strpcCC),
CCDesc = c.Field<string>(m_strpcCCDesc),
CostItem = c.Field<string>(m_strpcCostItem)
}).Distinct();
but I need the distinct method to be case insensitive. What is throwing me here is the use of anonymous types.
Attempted Solution 1
If I had SomeClass which had concrete objects I could obviously do
public class SumObject
{
public string CCType { get; set; }
public string CC { get; set; }
public string CCDesc { get; set; }
public string CostItem { get; set; }
}
I could obviously do this
List<SumObject> lso = new List<SumObject>()
{
new SumObject() { CCType = "1-OCC", CC = "300401", CCDesc = "Rooney", CostItem = "I477" },
new SumObject() { CCType = "1-OCC", CC = "300401", CCDesc = "Zidane", CostItem = "I677" },
new SumObject() { CCType = "1-OCC", CC = "300401", CCDesc = "Falcao", CostItem = "I470" },
};
var e = lso.Distinct(new SumObjectComparer()); // Great :]
where
class SumObjectComparer : IEqualityComparer<SumObject>
{
public bool Equals(SumObject x, SumObject y)
{
if (Object.ReferenceEquals(x, y))
return true;
if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
return false;
return x.CCType.CompareNoCase(y.CCType) == 0 &&
x.CC.CompareNoCase(y.CC) == 0 &&
x.CCDesc.CompareNoCase(y.CCDesc) == 0 &&
x.CostItem.CompareNoCase(y.CostItem) == 0;
}
public int GetHashCode(SumObject o)
{
if (Object.ReferenceEquals(o, null))
return 0;
int hashCCType = String.IsNullOrEmpty(o.CCType) ?
0 : o.CCType.ToLower().GetHashCode();
int hashCC = String.IsNullOrEmpty(o.CC) ?
0 : o.CC.ToLower().GetHashCode();
int hashCCDesc = String.IsNullOrEmpty(o.CCDesc) ?
0 : o.CCDesc.ToLower().GetHashCode();
int hashCostItem = String.IsNullOrEmpty(o.CostItem) ?
0 : o.CostItem.ToLower().GetHashCode();
return hashCCType ^ hashCC ^ hashCCDesc ^ hashCostItem;
}
}
However, the use of anonymous types in the above Linq query are throwing me.
Attempted Solution 2
To attempt another solution to this (and because I have the same issue elsewhere) I generated the following generic comparer class
public class GenericEqualityComparer<T> : IEqualityComparer<T>
{
Func<T, T, bool> compareFunction;
Func<T, int> hashFunction;
public GenericEqualityComparer(Func<T, T, bool> compareFunction, Func<T, int> hashFunction)
{
this.compareFunction = compareFunction;
this.hashFunction = hashFunction;
}
public bool Equals(T x, T y) { return compareFunction(x, y); }
public int GetHashCode(T obj) { return hashFunction(obj); }
}
so that I could attempt to do
var comparer = new GenericEqualityComparer<dynamic>(
(x, y) => { /* My equality stuff */ },
o => { /* My hash stuff */ });
but this casts the returned value as IEnumerable<dynamic> which in turn effects my forthcoming use of cflist, so that in a following query the join fails.
var cf =
(from o in cflist
join od in glext
on new { o.CCType, o.CC, o.CCDesc, o.CostItem } equals new
{
CCType = od.Field<string>(m_strpcCCType),
CC = od.Field<string>(m_strpcCC),
CCDesc = od.Field<string>(m_strpcCCDesc),
CostItem = od.Field<string>(m_strpcCostItem)
}
into c
select new { ... }
I don't want to get into ugly casting to and from IEnumerable<T>s due to the heavy use of this code...
Question
Is there a way I can create my an IEquailityComparer for my anonymous types?
Thanks for your time.
Is there a way I can create my an IEquailityComparer for my anonymous types?
Sure. You just need to use type inference. For example, you could have something like:
public static class InferredEqualityComparer
{
public static IEqualityComparer<T> Create<T>(
IEnumerable<T> example,
Func<T, T, bool> equalityCheck,
Func<T, int> hashCodeProvider)
{
return new EqualityComparerImpl<T>(equalityCheck, hashCodeProvider);
}
private sealed class EqualityComparerImpl<T> : IEqualityComparer<T>
{
// Implement in the obvious way, remembering the delegates and
// calling them appropriately.
}
}
Then:
var glext = m_dtGLExt.AsEnumerable();
var query = from c in glext
orderby ...
select new { ... };
var comparer = InferredEqualityComparer.Create(query,
(x, y) => { ... },
o => { ... }
);
var distinct = query.Distinct(comparer);
Basically the first parameter to the method is just used for type inference, so that the compiler can work out what type to use for the lambda expression parameters.
You could create the comparer ahead of time by creating a sample of the anonymous type:
var sample = new[] { new { ... } };
var comparer = InferredExqualityComparer.Create(sample, ...);
var distinct = (... query here ... ).Distinct(comparer);
but then any time you change the query you've got to change the sample too.
This post may get what you want. Although for .NET 2.0 it also works for newer versions (see the bottom of this post for how to achieve this). In contrast to Jon Skeets solution we won´t use a factory-method like create. But this is only syntactic sugar I think.
I'm trying to merge 2 lists using "Union" so I get rid of duplicates. Following is the sample code:
public class SomeDetail
{
public string SomeValue1 { get; set; }
public string SomeValue2 { get; set; }
public string SomeDate { get; set; }
}
public class SomeDetailComparer : IEqualityComparer<SomeDetail>
{
bool IEqualityComparer<SomeDetail>.Equals(SomeDetail x, SomeDetail y)
{
// Check whether the compared objects reference the same data.
if (Object.ReferenceEquals(x, y))
return true;
// Check whether any of the compared objects is null.
if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
return false;
return x.SomeValue1 == y.SomeValue1 && x.SomeValue2 == y.SomeValue2;
}
int IEqualityComparer<SomeDetail>.GetHashCode(SomeDetail obj)
{
return obj.SomeValue1.GetHashCode();
}
}
List<SomeDetail> tempList1 = new List<SomeDetail>();
List<SomeDetail> tempList2 = new List<SomeDetail>();
List<SomeDetail> detailList = tempList1.Union(tempList2, SomeDetailComparer).ToList();
Now the question is can I use Union and still get the record which has the latest date (using SomeDate property). The record itself can either be in tempList1 or tempList2.
Thanks in advance
The operation that is really suited to this purpose is an full outer join. The Enumerable class has an implementation of inner join, which you can use to find the duplicates and select whichever you prefer.
var duplicates = Enumerable.Join(tempList1, tempList2, keySelector, keySelector,
(item1, item2) => (item1.SomeDate > item2.SomeDate) ? item1 : item2)
.ToList();
keySelector is simply a function (could be a lambda expression) that extracts a key from an object of type SomeDetail. Now, to implement the full outer join, try something like this:
var keyComparer = (SomeDetail item) => new { Value1 = item.SomeValue1,
Value2 = item.SomeDetail2 };
var detailList = Enumerable.Union(tempList1.Except(tempList2, equalityComparer),
tempList2.Except(tempList1, equalityComparer)).Union(
Enumerable.Join(tempList1, tempList2, keyComparer, keyComparer
(item1, item2) => (item1.SomeDate > item2.SomeDate) ? item1 : item2))
.ToList();
equalityComparer should be an object that implements IEqualityComparer<SomeDetail> and effectively uses the keyComparer function for testing equality.
Let me know if that does the job for you.
You'd have to be able to tell Union how to pick which one of the duplicates to use. I don't know of a way to do that other than writing your own Union.
You cannot with the standard Union method, but you can create an extension method Union for List<SomeDetail> with this special handling and this method will be used because the signature fits better.
Why not just use HashSet<T>?
List<SomeDetail> tempList1 = new List<SomeDetail>();
List<SomeDetail> tempList2 = new List<SomeDetail>();
HashSet<SomeDetail> hs = new HashSet<SomeDetail>(new SomeDetailComparer());
hs.UnionWith(tempList1);
hs.UnionWith(tempList2);
List<SomeDetail> detailList = hs.ToList();
Merge generic lists
public static List<T> MergeListCollections<T>(List<T> firstList, List<T> secondList)
{
List<T> merged = new List<T>(firstList);
merged.AddRange(secondList);
return merged;
}
try this:
list1.RemoveAll(p => list2.Any(z => z.SomeValue1 == p.SomeValue1 &&
z => z.SomeValue2 == p.SomeValue1 &&
z => z.SomeDate == p.SomeDate));
var list3 = list2.Concat<SomeDetail>(list1).ToList();