PowerShell Weekly
PowerShell Weekly

PoshBytes: Arrays vs Lists

Matthew Dowst

PoshBytes: Arrays vs. Lists

What is the difference between Arrays and Lists, and SPOILER ALERT why you should use Lists.

This post is a companion for the video embedded below. Scroll down to see the code from the video.

Arrays: Creating and Appending

Arrays have a fixed size. Using += creates a new array each time.

$arr = 1,2,3
$arr

$arr += 4
$arr

Lists: Creating, Adding, and Editing In Place

Lists are dynamic. They support in-place add, insert, and remove operations.

$list = [Collections.Generic.List[string]]('alpha','beta','gamma')
$list

$list.Add('delta')
$list

$list.Insert(1,'between')
$list
$list.Remove('gamma')
$list
$list.RemoveAt(0)
$list

Indexing Helper Used In Examples

This helper function prints index and value for any collection that supports indexing and .Count.

Function Test-Array {
    param (
        $InputObject
    )

    for($i = 0; $i -lt $InputObject.Count; $i++) {
        Write-Host "$i - $($InputObject[$i])"
    }
}

Combining Collections: Arrays vs Lists

Start with two arrays

$a = 1,2,3
$b = 'A','B','C'

Combine using an Array accumulator

Each += creates a new array, then assigns it back.

$array = @()
$array += $a
$array += $b
Test-Array $array

Add arrays into a List using Add()

This produces a list of two elements where each element is an array.

$list = [Collections.Generic.List[object]]::new()
$list.Add($a)
$list.Add($b)
Test-Array $list

Flatten into a List using AddRange()

AddRange appends each element of the input arrays to the list.

$list = [Collections.Generic.List[object]]::new()
$list.AddRange($a)
$list.AddRange($b)
Test-Array $list

Key Points

  • Arrays are fixed-size. += creates a new array each time.
  • Lists are dynamic. Use .Add(), .Insert(), .Remove(), .RemoveAt(), and .AddRange().
  • Use arrays for small, fixed data or when an API specifically expects an array.
  • Use lists when you need frequent inserts and appends.
  • Both arrays and lists support indexing and .Count.

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