How to get sub-array from larger array in VB.NET?

Question

I have:

Dim arr() As String = {\"one\",\"two\",\"three\"}

I want a new array, sub, containing {\"one\", \"three\"} only. What

Answer 1

For this particular case, the simplest option is just to list the two items you want to copy:

Dim sub = {arr(0), arr(2)}

---

In the general case, if you want to take the first item, skip one item, and then take all the rest, an easy option would be to use the LINQ extension methods:

Dim sub = arr.Take(1).Concat(arr.Skip(2)).ToArray()

It yields

• {"one"} (arr.Take(1))
• concatenated with (Concat)
• {"three"} (arr.Skip(2))
• into a new array (ToArray())

Documentation:

• Enumerable.Take
• Enumerable.Skip

Answer 2

It's a little difficult to see what you want exactly, but something like this will work.

Dim arr() As String = {"one","two","three"}

Dim templist As New List(Of String)(arr)
templist.RemoveAt(1)
Dim sub() As String = templist.ToArray()

Personally, I'd be using List rather than String() if you want to make frequent changes like this.

---

EDIT: Considering RPK's comment below:

Function RemoveElements(ByVal arr() As String, ByVal ParamArray skip() As Integer) As String()
    Dim templist As New List(Of String)(arr.Length - skip.Length)
    For i As Integer = 0 to templist.Length - 1
        if Array.IndexOf(skip, i) = -1 Then templist.Add(arr(i))
    Next i
    Return templist.ToArray()
End Function

You can call this for a single element:

' Skips the second element.
Dim sub() As String = RemoveElements(arr, 1)

or with as many elements as you like:

' Skips the second, fourth, seventh and eleventh elements.
Dim sub() As String = RemoveElements(arr, 1, 3, 6, 10)

or with an array:

' Skips the second, fourth, seventh and eleventh elements.
Dim skip() As Integer = {1, 3, 6, 10}
Dim sub() As String = RemoveElements(arr, skip)

Note, this is slow code, but it can make your code easier to read and maintain.

Answer 3

You can use the Array.Copy method. I don't know how you are picking elements from your array. Are you randomly picking or any other way? But I think you need to create a second array and use the Copy method.

You can use the Copy method in a variety of ways. The link I gave above is to pick an element from a specified index of the first array and copy to a specified index of the second array.

Here is an example in C#:

string[] firstArray = {"dog","cat","fish","monkey"};
string[] secondArray = firstArray;
Array.Copy(firstArray,3,secondArray,0,1);
Console.WriteLine(secondArray[0].ToString());

A VB.NET example is here:

Arrays: Copy vs. Clone

In your case, you can put the Array.Copy in a loop and keep changing the source and destination index.