PowerShell function for adding elements to an array

Question

I\'m still quite new to PowerShell and am trying to create a few functions that weaves together for creating and administrating an array. And I\'m having some problems with

Answer 1

Arrays in .NET don't directly support insertion and they are normally fixed size. PowerShell does allow for easy array resizing but if the array gets large and you're appending (causing a resize) a lot, the performance can be bad.

One easy way to do what you want is to create a new array from the pieces e.g.:

if ($index -eq 0) {
    $MainArray = $add,$MainArray
}
elseif ($index -eq $MainArray.Count - 1) {
    $MainArray += $add
}
else {
    $MainArray = $MainArray[0..($index-1)], $add, $MainArray[$index..($MainArray.Length-1)]
}

But that is kind of a spew. I would use a List for this, which supports insertion and is more efficient than an array.

$list = new-object 'System.Collections.Generic.List[object]'
$list.AddRange((1,2,3,4,5))
$list.Insert(2,10)
$list

And if you really need an array, call the $list.ToArray() method when you're done manipulating the list.

Answer 2

Arrays don't have an .insert() method, but collections do. An easy way to produce a collection from an array is to use the .invoke() method of scriptblock:

$array = 5,5,4,5,5

$collection = {$array}.invoke()
$collection
$collection.GetType()

5
5
4
5
5

IsPublic IsSerial Name                                     BaseType                                  
-------- -------- ----                                     --------                                  
True     True     Collection`1                             System.Object                             

Now you can use the .insert() method to insert an element at an arbitrary index:

$collection.Insert(2,3)
$collection


5
5
3
4
5
5

If you need it to be an array again, an easy way to convert it back to an array is to use the pipeline:

$collection | set-variable array
$array
$array.GetType()

5
5
3
4
5
5

IsPublic IsSerial Name                                     BaseType                                  
-------- -------- ----                                     --------                                  
True     True     Object[]                                 System.Array