Nth element. In VB.NET we often use Lists of elements. Sometimes it can be useful to generate a List of every Nth element from our Lists.

List

With some modulo logic, we can test for every second element, third element or other distance. The Mod keyword, which is modulo division in VB.NET can be used here.

Mod

Example. We introduce a function EveryNthElement, which receives a List of strings, and returns another List of strings. The result is a collection containing the specified elements.

For

If

Module Module1
    Function EveryNthElement(list As List(Of String), n As Integer) As List(Of String)
        Dim result = New List(Of String)
        ' Step 1: loop over all indexes.
        For i As Integer = 0 To list.Count - 1
            ' Step 2: use a modulo expression, and add values if the result is 0.
            If i Mod n = 0
                result.Add(list(i))
            End If
        Next
        ' Step 3: return the list.
        Return result
    End Function

    Sub Main()
        ' Use the function on this list.
        Dim test = New List(Of String)({ "a", "b", "c", "d", "e", "f", "g", "h", "i" })
        
        Dim result = EveryNthElement(test, 2)
        Console.WriteLine(string.Join(",", result))
        
        Dim result2 = EveryNthElement(test, 3)
        Console.WriteLine(string.Join(",", result2))
    End Sub
End Module
a,c,e,g,i
a,d,g

Results. It is easy to determine that the function has correct output on the values 2 and 3. With 2, we skip over every other element. And with 3, we skip over 2 elements at a time.

A summary. Using modulo division (with the Mod keyword in VB.NET) allows us to test indexes with a distance between them. This allows us to sample all values separated with a specified distance.