Tutorial :Remove items from one list in another



Question:

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.


Solution:1

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.


Solution:2

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);  


Solution:3

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.


Solution:4

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:5

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();  


Solution:6

list1.RemoveAll(l => list2.Contains(l));  


Solution:7

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();  


Solution:8

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);              }          });  

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