Associate for map creation in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a map using the associate function.

Kotlin

val numbers = listOf(1, 2, 3)
val map = numbers.associate { it to [1] }

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

Ait - 1

Bit + 1

Cit * it

Dit / 2

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '*' for the value.

Forgetting to use 'to' to create a pair.

The associate function creates a map where each key is the element and the value is its square (it * it).

2fill in blank

medium

Complete the code to create a map where keys are strings and values are their lengths.

Kotlin

val words = listOf("apple", "banana", "cherry")
val map = words.associate { [1] to it.length }

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

Ait.length

Bit

C"word"

Dwords

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'it.length' as key instead of value.

Using a fixed string instead of the variable.

The key should be the word itself, so 'it' is used as the key.

3fill in blank

hard

Fix the error in the code to correctly create a map from a list of pairs.

Kotlin

val pairs = listOf("a" to 1, "b" to 2)
val map = pairs.associateBy [1]

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

A{ it.second }

Bit.first

Cit.second

D{ it.first }

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting curly braces around the lambda.

Using it.second instead of it.first for keys.

associateBy expects a lambda expression, so the key selector must be inside curly braces.

4fill in blank

hard

Fill both blanks to create a map where keys are words and values are their uppercase forms.

Kotlin

val words = listOf("dog", "cat", "bird")
val map = words.associate { [1] to [2] }

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

Ait

Bit.toUpperCase()

Cit.uppercase()

Dit.length

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'toUpperCase()' which is deprecated.

Using word length as value instead of uppercase string.

The key is the word itself (it), and the value is the uppercase form using 'uppercase()' in Kotlin.

5fill in blank

hard

Fill all three blanks to create a map from a list of words where keys are the first letter uppercase and values are the word length if length > 3.

Kotlin

val words = listOf("apple", "bat", "carrot", "dog")
val map = words.associate { [1] to [2] }
val filteredMap = map.filter { it.value [3] 3 }

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

Ait[0].uppercaseChar()

Bit.length

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'uppercase()' on a Char instead of 'uppercaseChar()'.

Using '<' instead of '>' in filter condition.

Keys are the first letter uppercase (it[0].uppercaseChar()), values are word length (it.length), and filter keeps values greater than 3.

Practice

1. What does the associate function do in Kotlin when used on a list?

easy

A. It filters elements based on a condition.

B. It creates a map by pairing each element with a key and value.

C. It sorts the list in ascending order.

D. It converts the list into a set.

Solution

1. Step 1: Understand the purpose of associate

   The associate function transforms a list into a map by creating key-value pairs from each element.

2. Step 2: Compare with other functions

   Sorting, filtering, and converting to a set are different operations and not what associate does.

3. Final Answer:

   It creates a map by pairing each element with a key and value. -> Option B

4. Quick Check:

   associate creates map = It creates a map by pairing each element with a key and value. [OK]

Hint: associate always creates a map from list elements [OK]

Common Mistakes:

• Confusing associate with sorting or filtering
• Thinking associate returns a list or set
• Assuming associate keeps duplicates as keys

2. Which of the following is the correct syntax to create a map from a list of strings listOf("a", "b") using associate where keys are the strings and values are their lengths?

easy

A. listOf("a", "b").associateWith { it }

B. listOf("a", "b").associate { it.length to it }

C. listOf("a", "b").associateBy { it.length }

D. listOf("a", "b").associate { it to it.length }

Solution

1. Step 1: Identify key-value pairing

   We want keys as strings and values as their lengths, so key = it, value = it.length.

2. Step 2: Match syntax

   associate { it to it.length } correctly pairs each element with its length.

3. Final Answer:

   listOf("a", "b").associate { it to it.length } -> Option D

4. Quick Check:

   key=string, value=length = listOf("a", "b").associate { it to it.length } [OK]

Hint: Use 'associate { key to value }' for custom map pairs [OK]

Common Mistakes:

• Swapping key and value in the pair
• Using associateBy or associateWith incorrectly
• Forgetting to use 'to' for pairs

3. What is the output of the following Kotlin code?

val list = listOf("cat", "dog", "bird")
val map = list.associate { it.first() to it.length }
println(map)

medium

A. Compilation error

B. {cat=3, dog=3, bird=4}

C. {c=3, d=3, b=4}

D. {c=3, d=3, b=3}

Solution

1. Step 1: Analyze the associate lambda

   Each element's first character is the key, and the length of the string is the value.

2. Step 2: Map entries

   "cat" -> 'c' to 3, "dog" -> 'd' to 3, "bird" -> 'b' to 4.

3. Final Answer:

   {c=3, d=3, b=4} -> Option C

4. Quick Check:

   Keys are first chars, values are lengths = {c=3, d=3, b=4} [OK]

Hint: associate uses lambda to create key-value pairs [OK]

Common Mistakes:

• Confusing keys with full strings
• Mixing up length values
• Expecting a list instead of a map

4. Identify the error in this Kotlin code snippet:

val numbers = listOf(1, 2, 3, 2)
val map = numbers.associate { it to it * 2 }
println(map)

medium

A. Later duplicate keys overwrite earlier ones silently.

B. Syntax error in associate lambda.

C. Duplicate keys cause runtime exception.

D. associate cannot be used with integers.

Solution

1. Step 1: Check for duplicate keys

   The list has duplicate '2' values, so key '2' appears twice.

2. Step 2: Understand associate behavior with duplicates

   associate overwrites earlier keys silently; no error occurs.

3. Final Answer:

   Later duplicate keys overwrite earlier ones silently. -> Option A

4. Quick Check:

   Duplicates overwrite silently = Later duplicate keys overwrite earlier ones silently. [OK]

Hint: Duplicate keys overwrite previous silently in associate [OK]

Common Mistakes:

• Expecting runtime error on duplicate keys
• Thinking associate syntax is wrong
• Believing associate can't handle integers

5. Given a list of pairs listOf("apple" to 1, "banana" to 2, "apple" to 3), how can you create a map that sums values for duplicate keys using associate or similar Kotlin functions?

hard

A. Use groupBy then mapValues to sum values.

B. Use associate directly; it sums duplicates automatically.

C. Use associateBy with a sum lambda.

D. Use associateWith to sum values.

Solution

1. Step 1: Understand associate limitation

   associate overwrites duplicate keys; it does not sum values.

2. Step 2: Use groupBy and mapValues

   Group pairs by key, then sum the values in each group to get combined totals.

3. Final Answer:

   Use groupBy then mapValues to sum values. -> Option A

4. Quick Check:

   Sum duplicates by grouping, not associate = Use groupBy then mapValues to sum values. [OK]

Hint: Sum duplicates by grouping, not associate [OK]

Common Mistakes:

• Expecting associate to sum duplicates
• Using associateBy incorrectly for summing
• Confusing associateWith purpose