How to compare 2 lists of objects and remove the items that are not common?

Question

I've got 2 generic lists that do not contain the all fields of the same type

IList<Category> and List<CategoriesRow>Categories

categoryList = IList<Category>

but both have common fields Name and ID.

I want to compare list Categories with categoryList and find from categoryList where categoryList[index].ID does not exist in the list of all Categories of ID. For all those that do not exist in Categories, I will have to remove them from CatgoryList.

I had a previous post in which I was given examples of LINQ, but the problem is I have to use Dynamic, implying that I am passing categoryList and Categories as Dynamic.

Can anyone give me an example how to go about the above as I have no idea how to do it.

Answer 1

First run a loop of all list element of CategoryList
Run the inner loop of all list element of Categories
Compare the id of CategoryList[index].ID with Categories[InnerIndex].ID
When the inner loop is finish, check if the condition is ever true in whole loop if so then the ID is exists in Categories otherwise not.

Answer 2

for (int i = categoryList.Count-1; i >= 0; i--)
{
  int id = categoryList[i].ID;
  if (!Categories.Any(r => r.ID == id)) categoryList.RemoveAt(i);
}

Answer 3

This might help you

for (int i = 0; i < CategoryList.Count; i++) { 
        if (!CategoryList.Contains(Categories[i]))
            Categories.RemoveAt(i);
        if (!Categories.Contains(CategoryList[i]))
            CategoryList.RemoveAt(i);
    }

Answer 4

public class Category
{
    public int Id;
}

public class CategoriesRow
{
    public int Id;
}

public List<Category> RemoveNotUsedCategories(List<Category> categoryList, List<CategoriesRow> Categories)
{
    List<Category> usedCategories = new List<Category>();

    foreach (Category usableCat in categoryList)
    {
        foreach (CategoriesRow catRow in Categories)
        {
            if (usableCat.Id == catRow.Id)
            {
                // Add categories that are used.
                usedCategories.Add(usableCat);
                // Will break the first loop.
                break;
            }
        }
    }
    return usedCategories;
}