Object arrays in PowerShell - Mini Project: Build & Apply

Working with Object Arrays in PowerShell

📖 Scenario: You are managing a small inventory system for a local bookstore. You want to keep track of books using PowerShell objects. Each book has a Title, Author, and Price. You will create an array of book objects, set a price limit, filter books below that price, and display the filtered list.

🎯 Goal: Build a PowerShell script that creates an array of book objects, sets a price limit, filters books cheaper than the limit, and prints the filtered books.

📋 What You'll Learn

Create an array of book objects with exact properties and values

Add a variable for the price limit

Filter the array to include only books cheaper than the price limit

Print the filtered list of books

💡 Why This Matters

🌍 Real World

Managing collections of items like books, products, or users is common in automation scripts. Object arrays let you organize and filter data easily.

💼 Career

PowerShell scripting with object arrays is useful for IT admins and automation engineers to handle system inventories, reports, and data filtering.

1

Create an array of book objects

Create an array called $books containing these three book objects with properties Title, Author, and Price: 'The Hobbit', 'J.R.R. Tolkien', 15.99; '1984', 'George Orwell', 12.5; 'Pride and Prejudice', 'Jane Austen', 9.99.

PowerShell

# Create the $books array with three book objects
# Your code here

Hint

Use [PSCustomObject] to create each book object and put them inside an array @( ... ).

2

Set a price limit variable

Create a variable called $priceLimit and set it to 13.

PowerShell

$books = @(
    [PSCustomObject]@{Title='The Hobbit'; Author='J.R.R. Tolkien'; Price=15.99},
    [PSCustomObject]@{Title='1984'; Author='George Orwell'; Price=12.5},
    [PSCustomObject]@{Title='Pride and Prejudice'; Author='Jane Austen'; Price=9.99}
)
# Create $priceLimit variable and set it to 13
# Your code here

Hint

Just assign the number 13 to the variable $priceLimit.

3

Filter books cheaper than the price limit

Create a new variable called $affordableBooks that contains only the books from $books where the Price is less than $priceLimit. Use the Where-Object cmdlet with a script block comparing $_ object's Price property to $priceLimit.

PowerShell

$books = @(
    [PSCustomObject]@{Title='The Hobbit'; Author='J.R.R. Tolkien'; Price=15.99},
    [PSCustomObject]@{Title='1984'; Author='George Orwell'; Price=12.5},
    [PSCustomObject]@{Title='Pride and Prejudice'; Author='Jane Austen'; Price=9.99}
)
$priceLimit = 13
# Filter books cheaper than $priceLimit into $affordableBooks
# Your code here

Hint

Use Where-Object { $_.Price -lt $priceLimit } to filter the array.

4

Print the filtered list of affordable books

Print the $affordableBooks variable to display the filtered books.

PowerShell

$books = @(
    [PSCustomObject]@{Title='The Hobbit'; Author='J.R.R. Tolkien'; Price=15.99},
    [PSCustomObject]@{Title='1984'; Author='George Orwell'; Price=12.5},
    [PSCustomObject]@{Title='Pride and Prejudice'; Author='Jane Austen'; Price=9.99}
)
$priceLimit = 13
$affordableBooks = $books | Where-Object { $_.Price -lt $priceLimit }
# Print the $affordableBooks variable
# Your code here

Hint

Simply type $affordableBooks to print the filtered list.

Practice

1. What is an object array in PowerShell?

easy

A. A type of function that returns objects

B. A single object with many properties

C. A command to create new objects

D. A variable that holds multiple objects together in a list

Solution

1. Step 1: Understand the definition of object arrays

   An object array is a collection that holds many objects in one variable, like a list.

2. Step 2: Compare options with the definition

   Only A variable that holds multiple objects together in a list correctly describes an object array as a variable holding multiple objects.

3. Final Answer:

   A variable that holds multiple objects together in a list -> Option D

4. Quick Check:

   Object array = list of objects [OK]

Hint: Remember: arrays hold many items together [OK]

Common Mistakes:

• Confusing object arrays with single objects
• Thinking object arrays are commands
• Mixing arrays with functions

2. Which of the following is the correct way to create an empty object array in PowerShell?

easy

A. $array = ()

B. $array = @()

C. $array = new-object array

D. $array = {}

Solution

1. Step 1: Recall PowerShell syntax for empty arrays

   PowerShell uses @() to create an empty array.

2. Step 2: Check each option

   $array = @() uses @(), which is correct. $array = () uses (), which assigns $null, not an array. $array = new-object array is incorrect syntax. $array = {} uses {}, which creates a hashtable, not an array.

3. Final Answer:

   $array = @() -> Option B

4. Quick Check:

   Empty array syntax = @() [OK]

Hint: Use @() to create empty arrays in PowerShell [OK]

Common Mistakes:

• Using () which assigns null, not an array
• Confusing arrays with hashtables {}
• Trying to use new-object for arrays

3. What will be the output of this PowerShell code?

$array = @()
$array += 'apple'
$array += 'banana'
$array += 'cherry'
$array

medium

A. apple
banana
cherry

B. @('apple', 'banana', 'cherry')

C. apple banana cherry

D. Error: Cannot add to array

Solution

1. Step 1: Understand how += adds items to arrays

   Using += adds each string as a new element to the array.

2. Step 2: Output the array variable

   When output, PowerShell prints each element on a new line, so the output is three lines: apple, banana, cherry.

3. Final Answer:

   apple banana cherry -> Option A

4. Quick Check:

   Array elements print line by line [OK]

Hint: Arrays print each item on its own line [OK]

Common Mistakes:

• Expecting all items on one line separated by spaces
• Thinking += causes an error on arrays
• Confusing array output with string output

4. Identify the error in this PowerShell script:

$array = @()
$array += 'one'
$array = $array + 'two'
$array = $array + 3
$array

medium

A. No error; script runs and outputs all items

B. Using + operator on arrays causes error

C. Cannot add integer to string array

D. Array must be declared with fixed size

Solution

1. Step 1: Check adding different types to array

   PowerShell arrays can hold mixed types, so adding integer 3 is allowed.

2. Step 2: Check use of + operator on arrays

   Using + concatenates arrays or adds items; it works fine here.

3. Final Answer:

   No error; script runs and outputs all items -> Option A

4. Quick Check:

   PowerShell arrays accept mixed types and + works [OK]

Hint: PowerShell arrays can mix types and use + to add items [OK]

Common Mistakes:

• Thinking arrays only hold one data type
• Believing + operator causes errors on arrays
• Assuming arrays need fixed size

5. You have an array of objects representing people:

$people = @(
  [pscustomobject]@{Name='Alice'; Age=30},
  [pscustomobject]@{Name='Bob'; Age=25},
  [pscustomobject]@{Name='Carol'; Age=35}
)

How do you add a new person object with Name='Dave' and Age=40 to this array?

hard

A. $people = @($people, @{Name='Dave'; Age=40})

B. $people = $people + @{Name='Dave'; Age=40}

C. $people += [pscustomobject]@{Name='Dave'; Age=40}

D. $people.Add([pscustomobject]@{Name='Dave'; Age=40})

Solution

1. Step 1: Create a new person object correctly

   Use [pscustomobject]@{Name='Dave'; Age=40} to create the new object.

2. Step 2: Add the new object to the existing array

   Use += to add the new object to the $people array. $people += [pscustomobject]@{Name='Dave'; Age=40} does this correctly.

3. Final Answer:

   $people += [pscustomobject]@{Name='Dave'; Age=40} -> Option C

4. Quick Check:

   Add object to array using += [OK]

Hint: Use += with new [pscustomobject] to add to array [OK]

Common Mistakes:

• Forgetting [pscustomobject] and adding plain hashtable
• Using .Add() which does not work on arrays
• Reassigning array incorrectly causing nested arrays