CODEWITHSUNDEEP
vb.net
Ari
Ari

Reputation: 6159

Remove an object from a List(of) based on object value

How do I remove an object from a list based on value, I'me getting an index out of range error

'A class called Person exists'
Dim PersonOne As New Person
PersonOne.name = "John"
PersonOne.age = 50

'Created a list to store them'
Dim MyList As New List(Of Person)
MyList.Add(PersonOne)

'Now to remove an object'
Dim ObjectToRemove As String = "John"

For Each item in MyList
    If String.Compare(item.name, ObjectToRemove) = 0 Then

        'How do I get the index to remove?'

    End If
Next

Excuse the code, I bashed it out off the top of my head, my original code is a bit more convoluted. But the gist is I just want to compare a value, if it matches remove that . object from the List(Of).

Upvotes: 0

Views: 246

Answers (1)

Dai
Dai

Reputation: 155055

Use the FindIndex method which accepts a predicate delegate. You can pass a lambda function for the predicate delegate.

(Also, I think it's clearer to use String.Equals with an explicit StringComparison instead of using String.Compare(x,y) == 0 as it signals intent better).

Dim personOneHasThisIndex As Integer
personOneHasThisIndex = MyList.FindIndex( Function(p) p.name.Equals( ObjectToRemove, StringComparison.Ordinal ) )

If personOneHasThisIndx > -1 Then
    ' Always check if the result is -1, which means it doesn't exist
    MyList.RemoveAt( personOneHasThisIndex )

End If

Note that List<T>.RemoveAt(Int32 index) is inefficient because it has to move every element in the List (lists cannot have "empty" spaces). If you have a conceptual list you'll be adding and removing from a lot, consider using LinkedList or a HashSet (if the order of the elements doesn't matter) instead.

Upvotes: 2

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