Hash tables (dictionaries) in PowerShell - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an empty hash table in PowerShell.

PowerShell

$hashTable = [1]

Drag options to blanks, or click blank then click option'

A[]

B@{}

C{}

D()

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets [] which create arrays, not hash tables.

Using just curly braces {} which is not valid for hash tables in PowerShell.

In PowerShell, an empty hash table is created using @{}.

2fill in blank

medium

Complete the code to add a key-value pair 'Name' = 'Alice' to the hash table.

PowerShell

$hashTable = @{}
$hashTable.[1] = 'Alice'

Drag options to blanks, or click blank then click option'

AKey

BAdd

CName

DValue

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to use 'Add' as a property name instead of the key.

Using 'Key' or 'Value' which are not valid property names.

To add a key-value pair, use the key name as a property: $hashTable.Name = 'Alice'.

3fill in blank

hard

Fix the error in the code to retrieve the value for key 'Age' from the hash table.

PowerShell

$age = $hashTable[1]'Age'

Drag options to blanks, or click blank then click option'

A['Age']

B.Age

C('Age')

D[Age]

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation with quotes which causes errors.

Using parentheses which is invalid syntax here.

To access a hash table value by key, use square brackets with the key as a string: $hashTable['Age'].

4fill in blank

hard

Fill both blanks to create a hash table with keys 'City' and 'Country' and values 'Paris' and 'France'.

PowerShell

$location = @[1] = '[2]'}

Drag options to blanks, or click blank then click option'

A'City'

B'Country'

CParis

DFrance

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around the key string.

Using commas instead of '=' to separate key and value.

To create a hash table with one key-value pair, use @{'City' = 'Paris'}. Here we fill the first blank with the key and the second with the value.

5fill in blank

hard

Fill all three blanks to create a hash table with keys 'Fruit' and 'Color' and values 'Apple' and 'Red'.

PowerShell

$fruitInfo = @[1] = '[2]'; [3] = 'Red'}

Drag options to blanks, or click blank then click option'

A'Fruit'

BApple

C'Color'

D'Red'

Attempts:

3 left

💡 Hint

Common Mistakes

Using commas instead of semicolons to separate pairs.

Not quoting the keys.

The hash table has two key-value pairs separated by semicolons. The first key is 'Fruit' with value 'Apple', the second key is 'Color' with value 'Red'.

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