powershell arraylist methods

How to create an ArrayList from an Array in PowerShell?

stackoverflow.com › questions › 618618 › how-to-create-an-arraylist-from-an-array-in-powershell

I can't get that constructor to work either. This however seems to work:

# $temp = Get-ResourceFiles
$resourceFiles = New-Object System.Collections.ArrayList($null)
$resourceFiles.AddRange($temp)

You can also pass an integer in the constructor to set an initial capacity.

What do you mean when you say you want to enumerate the files? Why can't you just filter the wanted values into a fresh array?

Edit:

It seems that you can use the array constructor like this:

$resourceFiles = New-Object System.Collections.ArrayList(,$someArray)

Note the comma. I believe what is happening is that when you call a .NET method, you always pass parameters as an array. PowerShell unpacks that array and passes it to the method as separate parameters. In this case, we don't want PowerShell to unpack the array; we want to pass the array as a single unit. Now, the comma operator creates arrays. So PowerShell unpacks the array, then we create the array again with the comma operator. I think that is what is going on.

Answer from dan-gph on Stack Overflow

Adam the Automator

adamtheautomator.com › powershell-array

PowerShell Arrays, ArrayLists & Collections: Best Practices

PS51> $MyArrayList = New-Object ... the elements at creation time or add them ad-hoc. To add elements to an existing collection, you can use the += operator or the Add method....

Published April 22, 2025

SPGuides

spguides.com › powershell-arraylist

PowerShell ArrayList [Create and Use]

March 26, 2025 - If you have an existing array and want to convert it to an ArrayList, you can use the AddRange() method. Here’s an example and the complete PowerShell:

Discussions

How to create an ArrayList from an Array in PowerShell? - Stack Overflow

To get an instance this would actually ... but I didn't check if powershell always uses ArrayList as the instance of array. 2016-02-22T23:51:03.41Z+00:00 ... @npjohns PowerShell arrays are actually .NET arrays. (The @().Add method fails.)... More on stackoverflow.com

stackoverflow.com

Adding arrays to arraylists

I have an object which is of type {system.collections.arraylist] To add a single element I can use the Add method but to add an array I have to use the ‘+=’ method. Does anyone have a technical explanation for this as ‘+=’ doesnt seem to be in the microsoft doco below: I am also assuming ... More on forums.powershell.org

forums.powershell.org

7

0

July 11, 2022

Two ways of creating a new System.Collections.ArrayList object, what's the difference?

Yes, you create an empty array then use it to initialize the variable. Two other ways (System not needed as its namespace is already loaded): [Collections.ArrayList]$list = @() $list = [Collections.ArrayList]::new() New-Object is useful when you need -ComObject, or to dynamically create a type (typename stored as a string that you may not know when writing). It is the 'older' method before powershell had classes built-in. Also, if you create an 'untyped' variable from a cast, you can change its type later on. The first example I posted enforces the type for that variable, it can only be an arraylist. I recommend using the generic types where you can specify the type: [Collections.Generic.List[String]]$list = @() $list = [Collections.Generic.List[Int]]::new() Also save some typing and use a namespace: using namespace System.Collections.Generic [List[String]]$list = @() $list = [List[Int]]::new() And for speed (enumeration access), if the items are unique, try a HashSet: using namespace System.Collections.Generic [HashSet[String]]$list = @() $list = [HashSet[Int]]::new() You should be measuring speed on insertion/removal and access for real world speed tests. And you'll definitely see different results when you go past milestones like 10, 1000, 10000 items (generics are tailored to large datasets). More on reddit.com

r/PowerShell

11

27

April 7, 2023

When to use array vs array list vs list

Array: When you don't need to dynamically add items to a collection outside a loop. ArrayList: Never. Generic list: When you do need to dynamically add items to a collection outside a loop. Arrays are the default output type in PowerShell. Whenever you run an expression that outputs multiple items you will get a System.Object array. An obvious example of this would be running a command like $Data = Get-ChildItem, a less obvious example would be the output from a loop: $Data = foreach ($Item in $Collection) or even an if/else statement $Data = if ($true) {"Hello"} else {"Goodbye"}. If the expression only outputs a single item then the array will get unwrapped and you just get the raw value like a string. Because it's the default behavior you don't really need to think about it but if you need more complex stuff that can't be handled by simply putting $Var = in front of an expression then you need a list. An easy example to demonstrate is an odd/even list: $Odd = [System.Collections.Generic.List[int]]::new() $Even = [System.Collections.Generic.List[int]]::new() foreach ($Number in 1..10) { if ($Number % 2 -eq 0) { $Even.Add($Number) } else { $Odd.Add($Number) } } More on reddit.com

r/PowerShell

40

33

April 25, 2022

Videos

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PowerShell 7 Tutorial 7: Introduction to Array and ArrayList - YouTube

February 20, 2023

31:38

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PowerShell 7 Tutorials for Beginners #3 : Array & ArrayList - YouTube

PowerShell Array and ArrayList - storing multiple items as a one ...

August 23, 2021

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Vexx32

vexx32.github.io › 2020 › 02 › 15 › Building-Arrays-Collections

Building Arrays and Collections in PowerShell

Why would we use this over ArrayList? In PowerShell there isn't a massive difference here, but for me personally it comes down to a few things. You can create a List that only stores a specific type, which means you can catch mistakes earlier. Adding other types of items to that list will either have them converted to the List's designated type, or will throw an error stating that it was the wrong type. Using the Add() method on List<T> doesn't create incidental output like ArrayList's Add() method does, so you have less chance to miss things and pollute your output stream.

SharePoint Diary

sharepointdiary.com › sharepoint diary › powershell › powershell tutorials › powershell arraylist – a beginners guide!

PowerShell ArrayList - A Beginners Guide! - SharePoint Diary

September 30, 2025 - These methods include adding elements, removing elements, sorting, and searching, among others. PowerShell ArrayList and Array are two collection types that can be used to store and manipulate data in PowerShell.

Stack Overflow

stackoverflow.com › questions › 618618 › how-to-create-an-arraylist-from-an-array-in-powershell

How to create an ArrayList from an Array in PowerShell? - Stack Overflow

Top answer

1 of 2

46

I can't get that constructor to work either. This however seems to work:

# $temp = Get-ResourceFiles
$resourceFiles = New-Object System.Collections.ArrayList($null)
$resourceFiles.AddRange($temp)

You can also pass an integer in the constructor to set an initial capacity.

What do you mean when you say you want to enumerate the files? Why can't you just filter the wanted values into a fresh array?

Edit:

It seems that you can use the array constructor like this:

$resourceFiles = New-Object System.Collections.ArrayList(,$someArray)

Note the comma. I believe what is happening is that when you call a .NET method, you always pass parameters as an array. PowerShell unpacks that array and passes it to the method as separate parameters. In this case, we don't want PowerShell to unpack the array; we want to pass the array as a single unit. Now, the comma operator creates arrays. So PowerShell unpacks the array, then we create the array again with the comma operator. I think that is what is going on.

2 of 2

36

Probably the shortest version:

[System.Collections.ArrayList]$someArray

It is also faster because it does not call relatively expensive New-Object.

Microsoft Learn

learn.microsoft.com › en-us › powershell › scripting › learn › deep-dives › everything-about-arrays

Everything you wanted to know about arrays - PowerShell | Microsoft Learn

If the only data that you have in your array is strings, then also take a look at using StringBuilder. It's almost the same thing but has some methods that are just for dealing with strings. The StringBuilder is specially designed for performance. It's common to see people move to ArrayList from arrays.

| How

pipe.how › new-arraylist

PowerShell Collections: ArrayList | How

January 17, 2020 - PipeHow:\Blog> $ArrayList = New-Object System.Collections.ArrayList PipeHow:\Blog> $ArrayList = [System.Collections.ArrayList]::new() One uses New-Object and the other calls the constructor of the class. You’re free to use whichever you prefer, although when sharing scripts it might be worth considering that people that are just getting into PowerShell and learning commands may be confused at the second one.

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LazyAdmin

lazyadmin.nl › home › how to use powershell array – complete guide

How to Use PowerShell Array - Complete Guide — LazyAdmin

January 19, 2023 - Learn how to create and use an Array in PowerShell. Including add and removing items, using the ArrayList and sorting arrays

IDERA

idera.com › home › using efficient lists in powershell

Using Efficient Lists in PowerShell | IDERA

April 22, 2025 - # use a dynamically extensible array $array = [System.Collections.ArrayList]@() 1..100000 | ForEach-Object { # use the Add() method instead of "+=" # discard the return value provided by Add() $null = $array.Add("adding $_") } $array.count

Varonis

varonis.com › blog › powershell-array

PowerShell Array Guide: How to Use and Create

June 9, 2022 - Here, we can use the default .Net constructor to create a new ArrayList, and then using the -Add operator to add items to it. The [void] operator is there because sometimes these commands throw out strange outputs that can mess with the code. These are the most common array types in PowerShell, but there are a few others.

SS64

ss64.com › ps › syntax-arrays.html

Create and use PowerShell Arrays

$countries = New-Object System.Collections.ArrayList $countries.Add('India') > $null $countries.Add('Montenegro') > $null · To retrieve an element, specify its number, PowerShell automatically numbers the array elements starting at 0.

PowerShell Forums

forums.powershell.org › powershell help

Adding arrays to arraylists - PowerShell Help - PowerShell Forums

July 11, 2022 - I have an object which is of type {system.collections.arraylist] To add a single element I can use the Add method but to add an array I have to use the ‘+=’ method. Does anyone have a technical explanation for this as ‘+=’ doesnt seem to be in the microsoft doco below: I am also assuming ...

Microsoft Certified Professional Magazine

mcpmag.com › articles › 2019 › 04 › 10 › managing-arrays-in-powershell.aspx

Managing Arrays in PowerShell -- Microsoft Certified Professional Magazine Online

Remove() methods to add or remove items from the array. I'm using the term "array" loosely here. From now on, a PowerShell array and an object of type · System.Collections.ArrayList is one and the same for us.

Wit IT

witit.blog › array-vs-arraylist-powershell

Array vs ArrayList (PowerShell) - Wit IT - witit

December 22, 2022 - Ouch, nothing but love for all of the PowerShell scripting politicians out there. I’m sure you’re the exception to this! Anyway, let’s look at an ArrayList and how it differs from our usual Array. First, let’s look at an easy way to define it: [Collections.ArrayList]$ArrayList = @('thing1','thing2') Secondly, let’s check the type with the GetType() method...

Powershell Commands

powershellcommands.com › powershell-array-list

Mastering PowerShell Array List: A Quick Guide

June 14, 2024 - Here’s how you do it: $arrayList = New-Object System.Collections.ArrayList · This line initializes a new instance of an array list, ready for you to add items. Populating your array list is straightforward.

reddit.com › r/powershell › two ways of creating a new system.collections.arraylist object, what's the difference?

r/PowerShell on Reddit: Two ways of creating a new System.Collections.ArrayList object, what's the difference?

April 7, 2023 -

I've come across two ways of creating a new System.Collections.ArrayList object:

$arrA = New-Object System.Collections.ArrayList
$arrB = [System.Collections.ArrayList]@()

I have two questions:

for arrB, if I'm reading this right, @() is creating an empty array and then it's being cast into [System.Collections.ArrayList]?
Working with the created object is the same for me either way, but are there any differences I may be missing?

I made a quick test and casting was faster, but the difference is only noticeable when creating new arrays reaches the hundreds of thousands to millions (tested on an old A10-7870k). Doesn't really matter when I'm creating one array, but I thought it was mildly interesting.

$max = 100000
$ticksStart = (Get-Date).Ticks
for ($i = 0; $i -lt $max; $i++)
{
	$arrA = New-Object System.Collections.ArrayList
}
$ticksEnd = (Get-Date).Ticks
Write-Host 'arrA (ticks)	: ' ($ticksEnd - $ticksStart)

$ticksStart = (Get-Date).Ticks
for ($i = 0; $i -lt $max; $i++)
{
	$arrB = [System.Collections.ArrayList]@()
}
$ticksEnd = (Get-Date).Ticks
Write-Host  'arrB (ticks)	: ' ($ticksEnd - $ticksStart)
arrA (ticks)	:  64310000
arrB (ticks)	:  3170000