Remove elements from one list that are found in another

Question

This should be quite easy, however I am failing to see why all my methods are not working.

I have looked at all the solutions and used them appropriately however am not getting the result.

solutions include

Solution 1

Solution 2

Here is the code:

IEnumerable<feature> available = _repo.GetAvailableFeatures();

IEnumerable<feature> selected = _repo.GetSelectedFeatures();

Using Except

var filteredList = (available.Except(selected)).ToList;

Using Linq

var availableList = available.ToList();

var selectedList = selected.ToList();

availableList.RemoveAll(item => selectedList.Contains(item));

Using old fashion for

for (var i = 0; i < availableList.Count - 1; i++)

        {

            foreach (var t in selectedList)

            {

                if (availableList[i].Id == t.Id)

                {

                    availableList.RemoveAt(i);

                }

            }

        }

My Feature class looks like this:

public class Feature

{

 public int Id;

 public int Desc;

}

Can anyone see it my mistakes here?

Answer 1

When you use Except you need to define what "equal" means for the feature type. In your loop you define "equal" as "Ids are equal", so you could:

Override Equals and GetHashCode in the feature class
- This becomes the "default" definition of equal for the type
Define a class that implements IEqualityComparer<feature>
- This could be used only when that definition is needed
Use Where instead of Except:
```
var filteredList = available.Where(a => !selected.Any(s => s.Id == a.Id))
                            .ToList();
```
- Performance is sub-optimal but it is a simpler code solution if performance overall is not affected significantly.

Remove elements from one list that are found in another

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