say if I had multiple lists created to hold some value. For example:
List<string> ListA= new List<string>();
List<string> ListB= new List<string>();
List<string> ListC= new List<string>();
List<int> ListD= new List<int>();
List<int> ListE= new List<int>();
Are there anyway to clear all list with one-liner? Currently, I'm doing this:
ListA.Clear();
ListB.Clear();
ListC.Clear();
ListD.Clear();
ListE.Clear();
No - not really.
You could create an extension method for this or just move it to a function. Whether that would be better would depend on the situation.
Unless you have nested lists or a or something i would definitely not bother.
You could of course add them all to a collection, and use foreach to call .clear() on each list but again - this depends on the situation.
You could, and without using another collection:
foreach (var list in Enumerable.Range(0, 5).Select<int, IList>(i => i switch { 0 => ListA, 1 => ListB, 2 => ListC, 3 => ListD, 4 => ListE })) list.Clear();
Not that it's any more readable than using 5 lines.
A cleaner solution solution would be to define a helper method:
void Clear(params IList[] lists)
{
foreach (var list in lists) list.Clear();
}
Then:
Clear(ListA, ListB, ListC, ListD, ListE);
I can give you some longer uglier ways...
new List<IList>() { ListA , ListB, ListC, ListD, ListE }.ForEach(x => x.Clear());
and
public static void ClearAll(params IList[] lists)
=> lists.ToList().ForEach(x => x.Clear());
// usage
ClearAll(ListA , ListB, ListC, ListD, ListE);
However, instead of multiple lists, you could just 1 list and a custom class
Related
I am trying to concate List<> as follows-
List<Student> finalList = new List<Student>();
var sortedDict = dictOfList.OrderBy(k => k.Key);
foreach (KeyValuePair<int, List<Student>> entry in sortedDict) {
List<Student> ListFromDict = (List<Student>)entry.Value;
finalList.Concat(ListFromDict);
}
But no concatenation happens. finalList remains empty. Any help?
A call to Concat does not modify the original list, instead it returns a new list - or to be totally accurate: it returns an IEnumerable<string> that will produce the contents of both lists concatenated, without modifying either of them.
You probably want to use AddRange which does what you want:
List<Student> ListFromDict = (List<Student>)entry.Value;
finalList.AddRange(ListFromDict);
Or even shorter (in one line of code):
finalList.AddRange((List<Student>)entry.Value);
And because entry.Value is already of type List<Student>, you can use just this:
finalList.AddRange(entry.Value);
Other answers have explained why Concat isn't helping you - but they've all kept your original loop. There's no need for that - LINQ has you covered:
List<Student> finalList = dictOfList.OrderBy(k => k.Key)
.SelectMany(pair => pair.Value)
.ToList();
To be clear, this replaces the whole of your existing code, not just the body of the loop.
Much simpler :) Whenever you find yourself using a foreach loop which does nothing but build another collection, it's worth seeing whether you can eliminate that loop using LINQ.
You may want to read up the documentation on Enumerable.Concat:
Return Value
Type: System.Collections.Generic.IEnumerable
An IEnumerable that contains the concatenated elements of the two input sequences.
So you may want to use the return value, which holds the new elements.
As an alternative, you can use List.AddRange, which Adds the elements of the specified collection to the end of the List.
As an aside, you can also achieve your goal with a simple LINQ query:
var finalList = dictOfList.OrderBy(k => k.Key)
.SelectMany(k => k.Value)
.ToList();
As specified here, Concat generates a new sequence whereas AddRange actually adds the elements to the list. You thus should rewrite it to:
List<Student> finalList = new List<Student>();
var sortedDict = dictOfList.OrderBy(k => k.Key);
foreach (KeyValuePair<int, List<Student>> entry in sortedDict) {
List<Student> ListFromDict = (List<Student>)entry.Value;
finalList.AddRange(ListFromDict);
}
Furthermore you can improve the efficiency a bit, by omitting the cast to a List<T> object since entry.Value is already a List<T> (and technically only needs to be an IEnumerable<T>):
var sortedDict = dictOfList.OrderBy(k => k.Key);
foreach (KeyValuePair<int, List<Student>> entry in sortedDict) {
finalList.AddRange(entry.Value);
}
Concat method does not modify original collection, instead it returns brand new collection with concatenation result. So, either try finalList = finalList.Concat(ListFromDict) or use AddRange method which modifies target list.
I have a List containing the Id property of some objects.
I have a List where I need a new List but only objects that has an Id matching in List.
How to do this with best performance?
Using linq:
List<MyClass> results = mylist.FindAll(x => listOfIds.Contains(x.ID));
Or if listOfIds has many many records:
HashSet<int> hashedIds = new HashSet<int>(listOfIds);
List<MyClass> results = mylist.FindAll(x => hashedIds.Contains(x.ID));
Finding Ids in HashSet<T> is far more faster than List<T>
If you need to enumerate items one by one then:
IEnumerable<MyClass> results = mylist.Where(x => listOfIds.Contains(x.ID));
foreach(MyClass item in results)
{
// do your work
}
I know how to combine 2 lists together in C#, but suppose I have an IEnumerable of objects, each with a list. How do I create 1 huge list, concatenating all of the lists.
I basically want to do the following in Linq (more elegant)
//FakeObject has a list property
IEnumerable<FakeObject> objects = ...;
List<int> hugeList = new List<int>();
foreach(FakeObject object in objects)
{
List<int> list = object.list;
foreach(int i in list)
{
hugeList.Add(i)
}
}
Use SelectMany to flatten a collection of collections into one list:
var hugeList = objects.SelectMany(o => o.list);
or for an actual list:
List<int> hugeList = objects.SelectMany(o => o.list).ToList();
I have 3 .net Lists items, I need to merge them all into one, to order them and bind them to a datagrid. However, I need a way of indicating which original list each item came from, so that I can identify this in the datagrid (change color or font etc).
Can anyone suggest the best way to do this?
List<Foo> list1 = new List<Foo>();
List<Foo> list2 = new List<Foo>();
List<Foo> list3 = new List<Foo>();
var query = list1.Select(foo => new { foo, list = "list1" })
.Concat(list2.Select(foo => new { foo, list = "list2" }))
.Concat(list3.Select(foo => new { foo, list = "list3" }))
.OrderBy(item => item.foo); // whatever you need to order by
Expand the properties as needed.
Assuming that your lists contains items of classes that you can amend I'd suggest that you add a property to those classes that keeps track of which type of the 3 it is. Either as an enum or possibly a reference to the actual list that contained it if you might need to refer back.
If you're not able to do that but assuming that they do contain a name property or similar and it's a readonly grid, a very ugly way would be to add a specific prefix/postfix to the name that says where it came from and then just remove that prefix/postfix before showing it on the screen.
Simple solution, assuming you don't want to modify the original class, or it's a primitive, you can use anonymous types:
var resultList = list1.Select(value => new {value, list = list1})
.Concat(list2.Select(value => new {value, list = list2})
.Concat(list3.Select(value => new {value, list = list3})))
.ToList();
I'd go with something like this:
List<object> list1 = new List<object>();
List<object> list2 = new List<object>();
List<object> list3 = new List<object>();
List<KeyValuePair<int, object>> mergedList = new List<KeyValuePair<int, object>>();
mergedList.AddRange(list1.Select(obj => new KeyValuePair<int, object>(1, obj)));
mergedList.AddRange(list2.Select(obj => new KeyValuePair<int, object>(2, obj)));
mergedList.AddRange(list3.Select(obj => new KeyValuePair<int, object>(3, obj)));
The better solution though, would be to add a property to your object that is some kind of enumeration that tells you something about the object itself. The lists themselves are metadata of some sort - list1 is a list of X, not just a list, so all of it's elements should have some kind of notion of X.
I'm trying to figure out how to traverse a generic list of items that I want to remove from another list of items.
So let's say I have this as a hypothetical example
List<car> list1 = GetTheList();
List<car> list2 = GetSomeOtherList();
I want to traverse list1 with a foreach and remove each item in List1 which is also contained in List2.
I'm not quite sure how to go about that as foreach is not index based.
You can use Except:
List<car> list1 = GetTheList();
List<car> list2 = GetSomeOtherList();
List<car> result = list2.Except(list1).ToList();
You probably don't even need those temporary variables:
List<car> result = GetSomeOtherList().Except(GetTheList()).ToList();
Note that Except does not modify either list - it creates a new list with the result.
You don't need an index, as the List<T> class allows you to remove items by value rather than index by using the Remove function.
foreach(car item in list1) list2.Remove(item);
In my case I had two different lists, with a common identifier, kind of like a foreign key.
The second solution cited by "nzrytmn":
var result = list1.Where(p => !list2.Any(x => x.ID == p.ID && x.property1 == p.property1)).ToList();
Was the one that best fit in my situation.
I needed to load a DropDownList without the records that had already been registered.
Thank you !!!
This is my code:
t1 = new T1();
t2 = new T2();
List<T1> list1 = t1.getList();
List<T2> list2 = t2.getList();
ddlT3.DataSource= list2.Where(s => !list1.Any(p => p.Id == s.ID)).ToList();
ddlT3.DataTextField = "AnyThing";
ddlT3.DataValueField = "IdAnyThing";
ddlT3.DataBind();
I would recommend using the LINQ extension methods. You can easily do it with one line of code like so:
list2 = list2.Except(list1).ToList();
This is assuming of course the objects in list1 that you are removing from list2 are the same instance.
list1.RemoveAll(l => list2.Contains(l));
You could use LINQ, but I would go with RemoveAll method. I think that is the one that better expresses your intent.
var integers = new List<int> { 1, 2, 3, 4, 5 };
var remove = new List<int> { 1, 3, 5 };
integers.RemoveAll(i => remove.Contains(i));
Solution 1 : You can do like this :
List<car> result = GetSomeOtherList().Except(GetTheList()).ToList();
But in some cases may this solution not work. if it is not work you can use my second solution .
Solution 2 :
List<car> list1 = GetTheList();
List<car> list2 = GetSomeOtherList();
we pretend that list1 is your main list and list2 is your secondry list and you want to get items of list1 without items of list2.
var result = list1.Where(p => !list2.Any(x => x.ID == p.ID && x.property1 == p.property1)).ToList();
As Except does not modify the list, you can use ForEach on List<T>:
list2.ForEach(item => list1.Remove(item));
It may not be the most efficient way, but it is simple, therefore readable, and it updates the original list (which is my requirement).
I think it would be quick to convert list A to a dictionary and then foreach the second list and call DictA.Remove(item) otherwise I think most solutions will cause many iterations through list A either directly or under the covers.
If the lists are small, it probably won't matter.
In case you have two different list with different DataModals
List<FeedbackQuestionsModel> feedbackQuestionsList = new();
List<EmployeesFeedbacksQuestionsModel> employeeQuestionsList = new();
var resultList = feedbackQuestionsList.Where(p => !employeeQuestionsList.Any(x => x.Question == p.Question)).ToList();
feedbackQuestionsList = resultList.ToList();
Here ya go..
List<string> list = new List<string>() { "1", "2", "3" };
List<string> remove = new List<string>() { "2" };
list.ForEach(s =>
{
if (remove.Contains(s))
{
list.Remove(s);
}
});