--- title: PowerShell Arrays, ArrayLists & Collections: Best Practices description: Learn about PowerShell Arrays, ArrayLists, and Collections, and apply best practices for efficient scripting. canonical: https://adamtheautomator.com/powershell-array/ --- # PowerShell Arrays, ArrayLists & Collections: Best Practices > Learn about PowerShell Arrays, ArrayLists, and Collections, and apply best practices for efficient scripting. Source: https://adamtheautomator.com/powershell-array/ --- - PowerShell Arrays, ArrayLists & Collections: Best Practices Tap to hide Home - Tutorials - Guidebooks - Instructors - Get Paid to Write - Advertising - Recommended Resources - About Adam Search for: - - - - # PowerShell Arrays, ArrayLists & Collections: Best Practices Published:29 October 2019 - 6 min. read - PowerShell [](https://adamtheautomator.com/author/nate/) [Nathan Kasco](https://adamtheautomator.com/author/nate/) Read [more tutorials](https://adamtheautomator.com/author/nate/) by Nathan Kasco! [](https://specopssoft.com/product/specops-password-auditor/?utm_source=adamtheautomator&utm_medium=referral&utm_campaign=adamtheautomator_referral_na&utm_content=display) Audit Active Directory for stale users, weak passwords, and other security risks with [Specops Password Auditor](https://specopssoft.com/product/specops-password-auditor/?utm_source=adamtheautomator&utm_medium=referral&utm_campaign=adamtheautomator_referral_na&utm_content=text). Table of Contents - Prerequisites/Requirements - Creating Arrays with PowerShellBuilding Arrays via Comma-Separated Elements - Using the Sub-Expression Operator - Using the Range Operator - Creating PowerShell ArrayList Collections - Adding Items To An Array - Removing Items From An Array - Retrieving Specific Items From An Array or ArrayList - Optimizing Arrays with PowerShell - Further Reading XFacebookLinkedIn Often times when writing PowerShell scripts, you need a way to store a set of items. One common way to achieve this is with an array or specific type known as an ArrayList. But what is an array anyway? An array is a data structure that is designed to store a collection of items. This can include both same and different types of items. Not a reader? Watch this related video tutorial! Not seeing the video? Make sure your ad blocker is disabled. Arrays are used in many different programming languages and PowerShell is no different. There are many ways to create, manipulate, and optimize arrays. In this article you will learn about ArrayLists, Arrays, and Collections as well as some best practices when applying them with PowerShell. ## Prerequisites/Requirements Since you’ll just be working with the PowerShell language itself, there are no environmental prerequisites. You just need to have a Windows PC with PowerShell. More specifically: - Windows PowerShell 3 or later - .NET Framework 4.5 or later Want more tips like this? Check out my personal PowerShell blog at: [https://nkasco.com/FriendsOfATA](https://nkasco.com/FriendsOfATA) ## Creating Arrays with PowerShell There are many different ways to create arrays with PowerShell. Let’s assume you have a list of names that you need to process somehow as shown below. John Susie Jim Johnny Carrie ### Building Arrays via Comma-Separated Elements The most basic way you can create an array is to simply assign known inputs, comma-separated, to a variable as shown below. $BasicArray = "John", "Susie", "Jim", "Johnny", "Carrie" If you run the GetType() method available on all objects in PowerShell, you will see that you have successfully created an array as indicated by the BaseType property shown below. PS51> $BasicArray.GetType() IsPublic IsSerial Name BaseType -------- -------- ---- -------- True True Object[] System.Array ### Using the Sub-Expression Operator You can also [create arrays in PowerShell via](https://adamtheautomator.com/teams-webhooks/) a sub-expression operator. This concept is commonly used when you don’t know how many items will be added to your array. The result can contain zero, or many items when created. Notice below an array called $MyArray has been created with zero elements inside. #Create an empty array with the sub-expression operator PS51> $MyArray = @() PS51> $MyArray.count 0 ### Using the Range Operator Arrays aren’t just relegated to storing strings as shown above. You can also create arrays with other object types like integers. If you need an array of integers in sequential order, you can take a shortcut and use the range .. operator. Below you can see an array was created with the integers 2 through 5 with a single line of code. PS51> $NumberedArray = 2..5 PS51> $NumberedArray 2 3 4 5 ## Creating PowerShell ArrayList Collections Using a PowerShell ArrayList is also a way in which you can store a list of items with PowerShell. The ArrayList class is part of the System.Collections namespace within .NET. By creating a new object of this type you can then store objects within an ArrayList. Below you can see that you need to explicitly create an ArrayList object using the New-Object cmdlet or by casting a standard array to an ArrayList object. Notice that in this case the BaseType is an object whereas the above examples have BaseTypes of [Arrays](https://docs.microsoft.com/en-us/dotnet/api/system.array?view=netframework-4.8) which exhibit inheritance from the [Object](https://docs.microsoft.com/en-us/dotnet/api/system.object?view=netframework-4.8) class. Ultimately, PowerShell is providing access to the .NET type system. PS51> $MyArrayList = New-Object -TypeName "System.Collections.ArrayList" # Casting an array as an ArrayList is also a viable option PS51> $MyArrayList = [System.Collections.ArrayList]@() PS51> $MyArrayList.GetType() IsPublic IsSerial Name BaseType -------- -------- ---- -------- True True ArrayList System.Object ## Adding Items To An Array When creating an array, you can either define all of 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. But know that there are major differences to how they operate. When you create a standard array with @(), you’ll use the += operator but to add elements to an ArrayList, you’d use the Add method. These methods differ in that the += operator actually destroys the existing array and creates a new one with the new item. To demonstrate, you’ll see below you can reference the IsFixedSize property for an array or ArrayList to know which is immutable and which is not. PS51> $BasicArray.IsFixedSize True PS51> $MyArrayList.IsFixedSize False Since a basic array is a collection of fixed size, you cannot modify it. Attempting to use the Add() method with an array that is fixed size will result in an error due to the fixed size. Below you can see a few examples in which you can successfully add items to an array. #Does NOT work $BasicArray.Add("Nate") #Works $BasicArray += "Nate" $MyArrayList.Add("Nate") $MyArrayList += "Nate" ## Removing Items From An Array Now that you have a better understanding of how to add items to an array, let’s cover a few ways you can remove items from an array. Since a basic array is fixed, you cannot remove items from them. Instead, you have to create an entirely new array. For example, you can remove a single element from an array by creating a conditional statement that only matches those elements you’d like to include. An example is shown below. $NewBasicArray = $BasicArray -ne "Nate" Since an ArrayList isn’t fixed, you can remove elements from them using the Remove() method. This is one scenario in which using an ArrayList may benefit you if you plan to be frequently adding/removing items. $MyArrayList.Remove("Nate") ## Retrieving Specific Items From An Array or ArrayList To retrieve specific items from an array or ArrayList you can use many different methods. Much like other objects in PowerShell, you can access all elements of an array by simply calling the object. PS51> $BasicArray John Susie Jim Johnny Carrie Perhaps you need to only retrieve the first element, arrays will always have an origin of 0 representing the first element of the array. To retrieve the first element of an array, specify the index number in brackets as shown below. PS51> $BasicArray[0] John Conversely, you can also reference indexes backwards by using a dash (negative indicator) to call the last X number of elements from the array. A common way to find the last element in an array is using -1 as shown below. PS51> $BasicArray[-1] Carrie The range operator that you learned about above can also be used to retrieve objects of an array by following the same method of calling the elements. Let’s say you want to retrieve the first four names in the $BasicArray array. You can see below you can specify a range of indexes 0-3 which will return the first four elements. PS51> $BasicArray[0..3] John Susie Jim Johnny ## Optimizing Arrays with PowerShell Now that you have a good foundation of how to create and manipulate arrays, which one should you use? To answer that, let’s walk through a few examples with the [Measure-Command](https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.utility/measure-command?view=powershell-5.1) cmdlet. Using the Measure-Command cmdlet, you’ll better understand how long commands are taking to process elements as they are passed down the pipeline. Generally speaking, if you have a small collection of objects you likely won’t notice much difference with how you manipulate your arrays. However, if you have a large collection of objects it is important to understand the differences to achieve optimal results. Let’s apply what you just learned in the prior section about the difference between += and using the Add() method with a loop of 50,000 items. First, create an empty array and an empty ArrayList as shown below. PS51> $MyArray = @() PS51> $MyArrayList = [System.Collections.ArrayList]@() Next, populate 50,000 elements in each collection using the range operator and a [foreach](https://adamtheautomator.com/powershell-foreach/) loop as shown below. @(0..50000).foreach({$MyArray += $_}) @(0..50000).foreach({$MyArrayList.Add($_)}) Finally, wrap your commands in an expression and pass that expression to the Measure-Command cmdlet. By executing the expression with Measure-Command, you can see how long each process actually takes to execute. Keep in mind that as you learned before, += actually creates a new array rather than appending to a fixed one. PS51> Measure-Command -Expression {@(0..50000).foreach({$MyArray += $_})} Days : 0 Hours : 0 Minutes : 0 Seconds : 59 Milliseconds : 58 Ticks : 590585963 TotalDays : 0.000683548568287037 TotalHours : 0.0164051656388889 TotalMinutes : 0.984309938333333 TotalSeconds : 59.0585963 TotalMilliseconds : 59058.5963 PS51> Measure-Command -Expression {@(0..50000).foreach({$MyArrayList.Add($_)})} Days : 0 Hours : 0 Minutes : 0 Seconds : 0 Milliseconds : 139 Ticks : 1399989 TotalDays : 1.62035763888889E-06 TotalHours : 3.88885833333333E-05 TotalMinutes : 0.002333315 TotalSeconds : 0.1399989 TotalMilliseconds : 139.9989 The result? Nearly 60 seconds versus 139 milliseconds! As you can see, it is much faster to leverage an ArrayList for large collections rather than using a fixed-size array. While this is a basic example, it stresses the importance of understanding what your code is doing during processing. If not properly understood, it can result in a poor user experience. If you have any existing script that could benefit from using an ArrayList rather than an array, this would present a fantastic opportunity to make an overnight improvement! ## Further Reading - Comparing arrays with PowerShell - How To Create Arrays for Performance in PowerShell (MCPmag) Want more tips like this? Check out my personal PowerShell blog at: [https://nkasco.com/FriendsOfATA](https://www.nkasco.com/). Hate ads? Want to support the writer? Get many of our tutorials packaged as an ATA Guidebook. [Explore ATA Guidebooks](https://adamtheautomator.com/ata-guidebooks/) ## More from ATA Learning and Partners - ### Recommended Resources! Recommended Resources for Training, Information Security, Automation, and more! - ### Get Paid to Write! ATA Learning is always seeking instructors of all experience levels. Regardless if you’re a junior admin or system architect, you have something to share. 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