Remove instances from a list by using LINQ or Lambda?
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 like this:
List<T> list;
List<T2> toBeRemovedItems;
// populate two lists
foreach(T2 item in toBeRemovedItems)
{
list.Remove(delegate(T one) {
// build a condition based on item
// return true or false
});
}
To be more specific, I actually build or populate toBeRemvoedItems list of a dynamic class (not a formal defined class). For example, the T class is something like MyClass and codes for removing are:
class MyClass<C> {
public string Value1 { get; set; }
public int Value2 { get; set; }
public C ObjectC { get; set; }
}
....
List<MyClass<C>> list;
// populate list
// populate toBeRemovedItems. Here is an example of hard-coded codes:
var toBeRemovedLItems = new[] {
new { Value1="a", Value2 = 1},
new { Value2="x", Value2 = 10},
...
};
// toBeRemovedItems may be the result of Select from a collection
foreach(var item in toBeRemovedLItems)
{
list.Remove(delegate(MyClass one) {
return one.Value1 = item.Value1 && one.Value2 < item.Value2;
});
}
I tried to search for Remove() method in IEnumerable interface from MSDN, but I cannot find the method of Remove() there (it makes sense that IEnumerable is used just for enumeration). In List class, there are several overloaded Remove(...) methods. I am not sure if there any alternative ways to remove items from a list by using LINQ or Lambda expressions?
By the way, I thought about a way to do a query against a list to get a subset or a new IEnumerable list with Where conditions, similar as moving items from a list. However, I prefer to remove items from my cached list, and there some cases I just cannot reset list property in a class to a new list (private set for example).
你可以使用RemoveAll方法：
MyClass one; //initialize MyClass
list.RemoveAll(item => one.Value1 == item.Value1 && one.Value2 < item.Value2);
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.
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.
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