PowerShell ArrayList – A Beginners Guide!

PowerShell ArrayList

Arrays provide a simple way to store a list of items in PowerShell, like other programming languages. However, standard PowerShell arrays have limitations – they are fixed-sized and don’t provide many helpful methods to manipulate the array contents. This is where ArrayLists come in. The ArrayList is one of the most useful collection types in PowerShell. It provides a dynamic array that can grow and shrink as needed. ArrayLists make it easy to add, remove, sort, and update items in the collection.

In this post, you will learn how to:

  • Create ArrayLists in PowerShell
  • Add, insert, and remove items from an ArrayList
  • Resize ArrayLists dynamically
  • Sort and reverse ArrayLists
  • Access items by index
  • Concatenate multiple ArrayLists
  • Convert between ArrayList and arrays
  • Search for items in an ArrayList

In this comprehensive guide, we will delve into the depths of the PowerShell ArrayList, from creation to manipulation, uncovering its features and benefits, troubleshooting common errors, and sharing tips to optimize your script performance.

Understanding ArrayList and its Benefits in PowerShell

powershell arraylist explained

Understanding how to work with ArrayLists unlocks more flexible scripting capabilities. The ArrayList is a generic List collection type found in the System.Collections.ArrayList class. You can store ordered collections of any object type, like strings, numbers, custom objects, etc. Unlike the traditional PowerShell array, ArrayList can grow and shrink dynamically, making it ideal for situations where the number of elements is not known in advance or needs to change over time.

The benefits of using an ArrayList in PowerShell are numerous:

  1. Dynamic size: As mentioned earlier, ArrayList can grow and shrink dynamically, unlike the traditional array in PowerShell. This means you can easily add or remove elements without worrying about resizing the array or losing data.
  2. Improved performance: ArrayList provides better performance compared to the traditional array, especially when dealing with large volumes of data. This is because ArrayList uses a more efficient method of storing and retrieving data, which reduces the time and resources required to process your scripts.
  3. Compatibility: ArrayList is compatible with other PowerShell objects and can be easily converted to different data types, such as strings or arrays. This makes it a versatile choice for working with various data sources and formats.
  4. Rich built-in methods: ArrayList provides several built-in methods for manipulating and processing data. These methods include adding elements, removing elements, sorting, and searching, among others.

PowerShell ArrayList vs. Array: Key differences

PowerShell ArrayList and Array are two collection types that can be used to store and manipulate data in PowerShell. While they share some similarities, they also have some key differences that set them apart.

  • ArrayList is a dynamic collection of objects that can grow and shrink dynamically, while Array is a static collection of objects with a fixed size. This means that once an Array is created, its size cannot be changed.
  • ArrayList provides better performance compared to Array when dealing with large volumes of data or when the number of elements is not known in advance. This is because ArrayList uses a more efficient method of storing and retrieving data, which reduces the time and resources required to process your scripts.
  • PowerShell Arrays are strongly typed (meaning they can only store elements of a specific type). In contrast, ArrayLists can store values of any data type.
  • On the other hand, Array offers better performance when dealing with a small number of elements or when the size of the collection is fixed. This is because Array uses a more straightforward method of storing and retrieving data, which can be faster than ArrayList in some cases.

When choosing between ArrayList and Array, consider the size and nature of your data, as well as the performance requirements of your script. Here is another post on using arrays in PowerShell: How to use Arrays in PowerShell?

Creating an ArrayList in PowerShell

Creating an ArrayList in PowerShell is a straightforward process. You can create an empty ArrayList using the following syntax:

$arrayList = New-Object -TypeName System.Collections.ArrayList

This initializes an empty ArrayList. Alternatively, you can use type accelerators to create a new array list variable:

$ArrayList = [System.Collections.ArrayList]::new()

Initialize ArrayList with a capacity: When creating an ArrayList, it’s a good idea to initialize it with a capacity close to the expected number of elements. This can help reduce the number of memory allocations and improve the performance of your script. For example, if you expect your ArrayList to have approximately 100 elements, you can create it like this:

$ArrayList = New-Object -TypeName System.Collections.ArrayList -ArgumentList 100

This creates an empty array list with 100 elements. Alternatively, you can create an ArrayList by casting a comma-separated list to [System.Collections.ArrayList]:

$ArrayList = [System.Collections.ArrayList]@("Banana", "Cherry", "Apple","Orange")

Both methods will create a new ArrayList object, which you can then use to store and manipulate data in your PowerShell script.

add to arraylist powershell

Unlike the default array, the ArrayList can contain a mix of data types. E.g., let’s say you want to create an “Employee” ArrayList with Employee Number, Employee Name, and Date of Join values:

$Employee = New-Object System.Collections.ArrayList
$Employee.Add(001)
$Employee.Add("Steve Johnson")
$Employee.Add([DateTime]"01/01/2021")

Adding elements to PowerShell ArrayList

Once your ArrayList is created, Adding elements to a PowerShell ArrayList is easy, with the help of the built-in Add() method. This method allows you to add a single element to the end of the ArrayList:

$ArrayList.Add("Berry")

Alternatively, you can use the AddRange() method to ArrayList with a set of initial values.

$Fruits = @("Banana", "Cherry", "Date")
$ArrayList.AddRange($Fruits)

For example, to create an ArrayList containing the numbers 1 to 5, you can use the following code:

$initialValues = 1..5
$arrayList = New-Object -TypeName System.Collections.ArrayList
$arrayList.AddRange($initialValues)

Here is another way to add multiple elements to an array list with the help of a Loop:

#Create a Array List
$ArrayList = New-Object System.Collections.ArrayList

#Add Elements to Array List
@(0..100).ForEach({$ArrayList.Add($_)})

Additionally, the Insert() method can be used to insert an element at a specific index within the ArrayList:

$arrayList.Insert(0, "Plums")

This code will insert “Plums” at the beginning of the ArrayList (index 0). Keep in mind that the index is zero-based, meaning that the first element has an index of 0, the second element has an index of 1, and so on.

You can use the GetType() method to retrieve the data type of an element stored in the ArrayList. E.g.,

$ArrayList[0].GetType().Name

Access and Retrieve Elements

To get the number of elements in ArrayList:

$ArrayList.Count

To retrieve an element by index:

$item1 = $Arraylist[0]
$item2 = $Arraylist[1]

You can access elements just like a standard PowerShell array.

To retrieve the last element:

$LastItem = $ArrayList[-1]

Loop Through ArrayList with Foreach

To process all elements in ArrayList, use Foreach:

ForEach ($Element in $ArrayList) {

  # Do something with $Element
  Write-Output $Element 

}

This iterates through each element sequentially. You can also use a for loop with Count:

For($i=0; $i -lt $Arraylist.Count; $i++) {
  # Do something with $element
  $element = $arraylist[$i]
  Write-host $Element
}

Here is another form:

$ArrayList | ForEach-Object {
    Write-Host $_
}

Modifying ArrayList elements in PowerShell

Once you have an ArrayList in your PowerShell script, there are several methods available to manipulate and modify its elements. To change the value of an element in an ArrayList, you can use the set_Item() method or the array index notation. For example, to update the first element, you can use:

$ArrayList.set_Item(0, "Updated Element") 

#Another way
$ArrayList[0] = "Updated Element".

We will explore more advanced manipulation techniques, such as sorting, reversing, and searching, in a later section of this article.

Removing elements from a PowerShell ArrayList

Removing elements from a PowerShell ArrayList is a common operation that can be done using the Remove(), RemoveRange() or RemoveAt() methods. Whether you want to remove a specific element, or multiple elements, or even clear the entire list, there’s a method to help you do just that. Here’s how:

The Remove() method removes the first occurrence of a specified element, while the RemoveAt() method removes the element at a specific index.

For example, to remove the first occurrence of the element “apple” from an ArrayList, you can use the following code:

$arrayList.Remove("apple")

Please note, that the above Remove method is case-sensitive. To remove the element at index 3, you can use the following code:

$ArrayList.RemoveAt(3)

Removing a Range of Elements

The RemoveRange method allows you to remove a range of elements by specifying the starting index and the number of elements to remove parameters:

$ArrayList.RemoveRange(0,2)  # This will remove the first two elements

To remove all items from the ArrayList, use the Clear() method:

$ArrayList.Clear()

Clear() empties the entire ArrayList.

Keep in mind that these methods modify the original Array List object, so use them with caution and ensure that you are removing the correct elements.

Sorting, reversing, and searching PowerShell ArrayLists

PowerShell ArrayList provides several methods for manipulating and processing data, such as sorting, reversing, and searching.

To sort an ArrayList, you can use the built-in Sort() method. For example, to sort an ArrayList of numbers in ascending order, you can use the following code:

$ArrayList.Sort()

To sort an ArrayList of strings in descending order, you can use the following code:

$ArrayList.Sort()
$ArrayList.Reverse()

This code will first sort the ArrayList in ascending order and then reverse the order to get the elements in descending order. The Sort-Object cmdlet also can be used for sorting elements in the array:

$SortedArrayList = $ArrayList | Sort-Object
sort arraylist powershell

To search for an element in an ArrayList, you can use the Contains() method. For example, to check if an ArrayList contains the element “apple”, you can use the following code:

if ($ArrayList.Contains("apple")) {
    Write-Host "ArrayList contains 'apple'"
}

This code will check if the ArrayList contains the element “apple” and print a message if it does. 

Convert Between ArrayList and Arrays

You can easily convert between ArrayList and standard PowerShell arrays:

Convert ArrayList to array

To convert an ArrayList to an array, use the typecasting as:

$Array = [array]$ArrayList

You can also use the ToArray() method:

$array = $arraylist.ToArray()

How about the reverse? To convert an existing array to ArrayList, use:

$arraylist = [System.Collections.ArrayList]$array

The array or ArrayList gets cast to the target type automatically.

Converting PowerShell ArrayList to string

There might be situations where you need to convert your PowerShell ArrayList to a string. This can be easily done using the -join operator or the String.Join() method. For example, to convert an ArrayList of strings to a single comma-separated string, you can use the following code:

$string = $arrayList -join ', '

Or, using the String.Join() method:

$string = [System.String]::Join(', ', $arrayList)

Both methods will create a new string containing the elements of the ArrayList, separated by the specified delimiter (a comma and a space in this case).

Join Multiple ArrayLists

To combine multiple ArrayLists:

$arraylist1 = [System.Collections.ArrayList]@(1, 2, 3)
$arraylist2 = [System.Collections.ArrayList]@(4, 5, 6)

$result = $arraylist1.Clone()
$result.AddRange($arraylist2)

Clone() makes a copy before appending $arraylist2 to avoid modifying the original.

Filter ArrayList

You can filter elements in ArrayList using the Where method:

#Create a Array List with values: 1 to 10
$Values = 1..10
$ArrayList = New-Object -TypeName System.Collections.ArrayList
$ArrayList.AddRange($Values)

#Filter Array List
$Arraylist = $ArrayList.Where{$_ -ge 5}

Alternatively, You can use the Where-Object cmdlet to Filter Array elements:

#Filter ArrayList
$MyArraylist = $ArrayList | Where-Object {$_ -ge 5}

Export ArrayList to CSV

Let’s say you have an ArrayList like this:

$ArrayList = New-Object System.Collections.ArrayList
$ArrayList.Add("Apple")
$ArrayList.Add("Banana")
$ArrayList.Add("Cherry")

The challenge here is that this ArrayList contains simple string data, and Export-Csv expects objects with properties. To resolve this, you could create a custom object array from these simple data types, like:

#Convert ArrayList to Object array
$Objects = $ArrayList | ForEach-Object { [PSCustomObject]@{Fruit = $_} }

#Export Array to CSV
$Objects | Export-Csv -Path "C:\Temp\Fruits.csv" -NoTypeInformation

PowerShell Import CSV to ArrayList

You can import a CSV file into an ArrayList using Import-Csv and a ForEach loop.

$csvData = Import-Csv -Path 'C:\Temp\Fruits.csv'
$ArrayList = New-Object System.Collections.ArrayList

ForEach ($row in $csvData) {
    $ArrayList.Add($row)
}

Common errors and troubleshooting in PowerShell ArrayList

As you work with PowerShell ArrayList, you may encounter some common errors or issues. In this section, we will discuss some of these errors and provide tips for troubleshooting and resolving them.

  1. Index out of range: This error occurs when you try to access or modify an element at an index that does not exist in the ArrayList. To avoid this error, always ensure that the index you are using is within the bounds of the ArrayList. You can use the Count property to get the number of elements in the ArrayList.
  2. InvalidCastException: This error occurs when you try to convert an element in the ArrayList to an incompatible data type. To fix this error, ensure that you are using the correct data type for the element in question or use the appropriate conversion methods provided by PowerShell and the .NET Framework.
  3. Adding elements of different data types: While it is possible to store elements of different data types in an ArrayList, doing so can lead to unexpected behavior and performance issues. To avoid this, try to use a consistent data type for all elements in the ArrayList or consider using a different collection type, such as a Hashtable or a custom object.

Real-world applications of PowerShell ArrayList

PowerShell ArrayList can be used in a variety of real-world scenarios, such as:

  1. Log file processing: ArrayList can be used to store and process log file data, allowing you to filter, sort, and analyze log entries efficiently.
  2. Inventory management: PowerShell ArrayList can be utilized to store and manage inventory data, such as computer names, IP addresses, and hardware details.
  3. Data processing: ArrayList can be employed in data processing tasks, such as parsing CSV files, processing XML data, or handling JSON objects.
  4. Script optimization: As mentioned earlier, using ArrayList can help improve the performance of your PowerShell scripts, making it a valuable tool for script optimization tasks.
  5. Storing ordered collections like lists of servers, users, etc., that change frequently
  6. Collecting output from loops and pipelines before exporting to CSV

Conclusion

ArrayLists provide a powerful alternative to standard PowerShell arrays for storing dynamic collections. In this comprehensive guide, we have covered the essentials of PowerShell ArrayList, from creation and manipulation to troubleshooting common errors of this fantastic data structure. We have also explored real-world use cases and provided tips for optimizing script performance. By understanding the features and benefits of ArrayList, you can easily store and manipulate data in a dynamic and efficient way.

Now that you have a solid understanding of PowerShell ArrayList, it’s time to put your knowledge into practice and start optimizing your scripts. Remember to follow best practices and leverage the built-in methods provided by ArrayList to get the most out of your PowerShell scripts.

If you want to learn more about PowerShell ArrayList and other PowerShell topics, consider exploring the following resources: Microsoft Docs – ArrayList Class

Salaudeen Rajack

Salaudeen Rajack - Information Technology Expert with Two-decades of hands-on experience, specializing in SharePoint, PowerShell, Microsoft 365, and related products. He has held various positions including SharePoint Architect, Administrator, Developer and consultant, has helped many organizations to implement and optimize SharePoint solutions. Known for his deep technical expertise, He's passionate about sharing the knowledge and insights to help others, through the real-world articles!

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