Hash tables (dictionaries) in PowerShell - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this PowerShell hash table access?

Consider the following PowerShell script:

$hash = @{ 'apple' = 3; 'banana' = 5; 'cherry' = 7 }
$result = $hash['banana']
Write-Output $result

What will be printed?

PowerShell

$hash = @{ 'apple' = 3; 'banana' = 5; 'cherry' = 7 }
$result = $hash['banana']
Write-Output $result

A 7

B 3

C 5

D banana

💡 Hint

Think about how to get the value for a key in a hash table.

The hash table stores keys and values. Accessing $hash['banana'] returns the value 5.

📝 Syntax

intermediate

Which option correctly creates a hash table with keys 'x' and 'y' and values 10 and 20?

Choose the correct PowerShell syntax to create a hash table with keys 'x' and 'y' and values 10 and 20 respectively.

A @{ 'x' : 10, 'y' : 20 }

B @{ x = 10; y = 20 }

C @{ 'x' = 10, 'y' = 20 }

D @{ x : 10; y : 20 }

💡 Hint

PowerShell uses = to assign values in hash tables, and semicolons separate pairs.

PowerShell hash tables use @{ key = value; key2 = value2 } syntax. Colons are not used.

🔧 Debug

advanced

Why does this PowerShell hash table script cause an error?

Look at this script:

$hash = @{ 'a' = 1; 'b' = 2 }
Write-Output $hash[a]

Why does it cause an error?

A Because 'a' is not quoted when accessing the hash table key

B Because the hash table keys must be integers

C Because Write-Output cannot print hash table values

D Because the hash table is empty

💡 Hint

Think about how keys are referenced in PowerShell hash tables.

Hash table keys must be quoted strings when accessed by string keys. Without quotes, PowerShell treats 'a' as a variable.

🚀 Application

advanced

How to add a new key-value pair to an existing PowerShell hash table?

You have this hash table:

$hash = @{ 'name' = 'Alice'; 'age' = 30 }

Which command correctly adds a new key 'city' with value 'Seattle'?

A $hash.Add('city', 'Seattle')

B Add-Item $hash 'city' 'Seattle'

C $hash += @{ 'city' = 'Seattle' }

D $hash['city'] = 'Seattle'

💡 Hint

Think about how to assign a new key in a hash table.

Assigning a new key-value pair is done by $hash['key'] = value. The Add() method exists for hashtables but throws an exception if the key already exists.

🧠 Conceptual

expert

What is the count of items in this PowerShell hash table after execution?

Consider this script:

$hash = @{ 'one' = 1; 'two' = 2 }
$hash['three'] = 3
$hash['two'] = 22
$hash.Remove('one')

How many key-value pairs remain in $hash?

A 2

B 3

C 1

D 4

💡 Hint

Count how many keys remain after adding, updating, and removing.

Initially 2 keys. Added 'three' (3 keys). Updated 'two' (still 3 keys). Removed 'one' (2 keys remain).

Practice

1. What is the correct way to create an empty hash table in PowerShell?

easy

A. ()

B. []

C. @{}

D. {}

Solution

1. Step 1: Understand hash table syntax in PowerShell

   PowerShell uses @{} to define hash tables, which store key-value pairs.

2. Step 2: Identify the empty hash table syntax

   An empty hash table has no key-value pairs inside, so it is @{}.

3. Final Answer:

   @{} -> Option C

4. Quick Check:

   Empty hash table = @{ } [OK]

Hint: Use @{} to create hash tables in PowerShell [OK]

Common Mistakes:

• Using {} which is a script block, not a hash table
• Using [] which is an array, not a hash table
• Using () which is for grouping or method calls

2. Which of the following is the correct syntax to add a key-value pair 'Name' = 'Alice' to an existing hash table $person?

easy

A. $person[Name] = 'Alice'

B. $person.Name = Alice

C. $person->Add('Name', 'Alice')

D. $person.Add('Name', 'Alice')

Solution

1. Step 1: Recall how to add key-value pairs to hash tables

   PowerShell hash tables have an Add() method to add new keys and values.

2. Step 2: Identify correct method call syntax

   The correct syntax is $person.Add('Name', 'Alice'). Note that the Add() method specifically adds new entries.

3. Final Answer:

   $person.Add('Name', 'Alice') -> Option D

4. Quick Check:

   Add key-value with Add() method [OK]

Hint: Use Add() method to add new keys to hash tables [OK]

Common Mistakes:

• Using -> which is not PowerShell syntax
• Using dot notation with unquoted value
• Using unquoted key in square brackets

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

$hash = @{ 'a' = 1; 'b' = 2 }
$hash['a'] = 3
$hash['c'] = 4
$hash['b']

medium

A. 2

B. 1

C. 3

D. 4

Solution

1. Step 1: Understand the initial hash table and updates

   The hash table starts with keys 'a' = 1 and 'b' = 2. Then 'a' is updated to 3, and a new key 'c' = 4 is added.

2. Step 2: Identify the value accessed

   The code outputs $hash['b'], which was never changed and remains 2.

3. Final Answer:

   2 -> Option A

4. Quick Check:

   Access unchanged key 'b' = 2 [OK]

Hint: Check which key is accessed after updates [OK]

Common Mistakes:

• Confusing updated key 'a' with accessed key 'b'
• Assuming last added key 'c' is accessed
• Mixing values of different keys

4. Identify the error in this PowerShell code snippet:

$ht = @{ 'x' = 10 }
$ht.Add('x', 20)

medium

A. Runtime error: key 'x' already exists

B. Syntax error in hash table creation

C. No error, code runs fine

D. Add method does not exist for hash tables

Solution

1. Step 1: Understand hash table initialization

   The hash table $ht is created with key 'x' = 10.

2. Step 2: Analyze the Add() method call

   Calling $ht.Add('x', 20) tries to add a duplicate key 'x', which causes a runtime error.

3. Final Answer:

   Runtime error: key 'x' already exists -> Option A

4. Quick Check:

   Adding duplicate key causes runtime error [OK]

Hint: Add() fails if key already exists in hash table [OK]

Common Mistakes:

• Assuming Add() updates existing keys
• Thinking Add() method doesn't exist
• Confusing syntax error with runtime error

5. You have a list of users and their ages:

$users = @('Alice', 'Bob', 'Charlie')
$ages = @(25, 30, 35)

Which PowerShell code correctly creates a hash table mapping each user to their age?

hard

A. $userAges = @{}; foreach ($user in $users) { $userAges.Add($user, $ages) }

B. $userAges = @{}; for ($i=0; $i -lt $users.Count; $i++) { $userAges[$users[$i]] = $ages[$i] }

C. $userAges = @{}; $users | ForEach-Object { $userAges.Add($_, $ages[$_]) }

D. $userAges = @{}; for ($i=0; $i -le $users.Count; $i++) { $userAges[$i] = $ages[$i] }

Solution

1. Step 1: Understand the goal

   Create a hash table where each user name is a key and their corresponding age is the value.

2. Step 2: Analyze each option

   $userAges = @{}; for ($i=0; $i -lt $users.Count; $i++) { $userAges[$users[$i]] = $ages[$i] } uses a for loop with index to assign each user key to the correct age value. $userAges = @{}; foreach ($user in $users) { $userAges.Add($user, $ages) } tries to add all ages at once, which is incorrect. $userAges = @{}; $users | ForEach-Object { $userAges.Add($_, $ages[$_]) } uses $_ as index but $_ is the user string, not an index. $userAges = @{}; for ($i=0; $i -le $users.Count; $i++) { $userAges[$i] = $ages[$i] } loops one too many times and uses numeric keys instead of user names.

3. Final Answer:

   $userAges = @{}; for ($i=0; $i -lt $users.Count; $i++) { $userAges[$users[$i]] = $ages[$i] } -> Option B

4. Quick Check:

   Use indexed loop to map keys to values [OK]

Hint: Use index loop to map two lists into hash table [OK]

Common Mistakes:

• Using foreach without index to access parallel array
• Using wrong loop bounds causing errors
• Assigning numeric keys instead of user names