Remove instances from a list by using LINQ or Lambda?

Question

Now I come a stage to get all my data as a list in cache(objects) and my next thing I have to do is to remove some instances from the list.

Normally, I would do removing

Answer 1

I agree with Jared's suggestion of filtering out certain items, but it looks like a join on Value1 would be a more efficient approach:

var res = from item1 in list
          join item2 in toBeRemovedList
            on item1.Value1 equals item2.Value1
          where item1.Value2 >= item2.Value2
          select item1;

Update: Apparently I fail at reading comprehension - new approach:

var removeDict = toBeRemovedList.ToDictionary(i => i.Value1, i => i.Value2);
list.RemoveAll(item => {
    int itemToRemoveValue2;
    if(removeDict.TryGetValue(item.Value1, out itemToRemoveValue2))
        return item.Value2 < itemToRemoveValue2;
    return false;
});

Of course, it would be even better if your list to remove could start as a dictionary. Ultimately, we're just trying to make our match on Value1 more efficient.

Answer 2

You could use the method RemoveAll:

MyClass one; //initialize MyClass
list.RemoveAll(item => one.Value1 == item.Value1 && one.Value2 < item.Value2);

Answer 3

You can use LINQ's Where method to filter out values that should not be a part of the list. The result is an IEnumerable<T> with the elements removed.

var res = list.Where(item => !(one.Value1 == item.Value1 && one.Value2 < item.Value2));

This will not updated the original List<T> instance but instead will create a new IEnumerable<T> with the values removed.

Answer 4

If I get the question correctly, to produce a unique set from two List.

For this, you can use the following

List list1; List list2;

List list3 = list1.Except(list2)

The list3 will contain unique items.

Answer 5

foreach(var item in toBeRemovedLItems) {   
   list.RemoveAll(one => one.Value1 == item.Value1 && one.Value2 < item.Value2); 
}

Too late again. Oh well.

Answer 6

For collections that are not lists (can't expose RemoveAll), you can still remove items with a one-liner.

To replace inline, just generate a list of items to remove, then run through it and execute remove code.

var dictionary = new Dictionary<string, string>(){{"foo", "0"}, {"boo", "1"}, {"goo", "1"}};
dictionary
    .Where(where_item =>
        ((where_item.Key == "foo") && (where_item.Value == "0"))
        || ((where_item.Key == "boo") && (where_item.Value == "1"))
    )
    .ToList()
    .ForEach(remove_item => {
        dictionary.Remove(remove_item.Key);
    });

To replace in copy, just generate a filtered enumerable and return a new copy.

var dictionary0 = new Dictionary<string, string>(){{"foo", "0"}, {"boo", "1"}, {"goo", "1"}};
var dictionary1 = dictionary0
    .Where(where_item =>
        ((where_item.Key == "foo") && (where_item.Value == "0"))
        || ((where_item.Key == "boo") && (where_item.Value == "1"))
    )
    .ToDictionary(each_item => each_item.Key, each_item => each_item.Value);