Zip for combining collections in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to combine two lists into pairs using zip.

Kotlin

val numbers = listOf(1, 2, 3)
val words = listOf("one", "two", "three")
val zipped = numbers.[1](words)
println(zipped)

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

Azip

Bmap

Cfilter

DflatMap

Attempts:

3 left

💡 Hint

Common Mistakes

Using map instead of zip will not combine two lists.

filter and flatMap do not combine two collections into pairs.

The zip function combines two collections into pairs of elements.

2fill in blank

medium

Complete the code to create a list of sums by zipping two lists and adding their elements.

Kotlin

val a = listOf(1, 2, 3)
val b = listOf(4, 5, 6)
val sums = a.zip(b) { x, y -> x [1] y }
println(sums)

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

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

Using division which may cause unexpected results.

The lambda adds elements from both lists to create sums.

3fill in blank

hard

Fix the error in the code to correctly zip two lists and print pairs.

Kotlin

val list1 = listOf("a", "b", "c")
val list2 = listOf(1, 2, 3)
val pairs = list1.[1](list2)
println(pairs)

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

AzipWith

Bzip

Ccombine

DpairWith

Attempts:

3 left

💡 Hint

Common Mistakes

Using zipWith which does not exist in Kotlin.

Using combine or pairWith which are invalid.

The correct function to combine two lists into pairs is zip.

4fill in blank

hard

Fill both blanks to create a zipped list of strings showing pairs separated by a dash.

Kotlin

val first = listOf("red", "green", "blue")
val second = listOf("apple", "leaf", "sky")
val combined = first.zip(second) { a, b -> a [1] "-" [2] b }
println(combined)

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

A+

B*

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' or '-' operators which do not concatenate strings.

Using only one '+' and missing the other concatenation.

Use '+' to concatenate strings in Kotlin.

5fill in blank

hard

Fill all three blanks to create a zipped map from two lists where keys are uppercase strings and values are their lengths.

Kotlin

val keys = listOf("cat", "dog", "bird")
val values = listOf(3, 4, 5)
val map = keys.zip(values).associate { (k, v) -> [1] to [2] }
val result = map.mapValues { it.value [3] 1 }
println(result)

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

Ak.uppercase()

Bv

C+

Dk.length

Attempts:

3 left

💡 Hint

Common Mistakes

Using k.length instead of uppercase for keys.

Not adding 1 to values in mapValues.

Mixing up keys and values in the associate lambda.

Keys are uppercase strings, values are original numbers, then 1 is added to each value.

Practice

1. What does the zip function do when used with two lists in Kotlin?

easy

A. Combines all elements from both lists into one longer list.

B. Pairs elements from both lists into a list of pairs, stopping at the shorter list length.

C. Creates a map from the first list's elements to the second list's elements without pairing.

D. Filters elements that are common to both lists.

Solution

1. Step 1: Understand the zip function behavior

   The zip function pairs elements from two collections by their positions.

2. Step 2: Consider the length of the resulting list

   The resulting list length equals the smaller of the two input lists, pairing elements until one list runs out.

3. Final Answer:

   Pairs elements from both lists into a list of pairs, stopping at the shorter list length. -> Option B

4. Quick Check:

   Zip pairs elements up to shortest list length [OK]

Hint: Zip pairs elements by index, stops at shortest list length [OK]

Common Mistakes:

• Thinking zip concatenates lists instead of pairing
• Assuming zip returns a map automatically
• Believing zip pairs all elements ignoring list length

2. Which of the following is the correct syntax to zip two lists listA and listB in Kotlin?

easy

A. val zipped = listA + listB.zip()

B. val zipped = zip(listA, listB)

C. val zipped = listA.zip(listB)

D. val zipped = listA.zipWith(listB)

Solution

1. Step 1: Recall Kotlin's zip syntax

   The zip function is called as an extension on the first list, passing the second list as argument.

2. Step 2: Check each option

   val zipped = listA.zip(listB) matches the correct syntax: listA.zip(listB). Others are invalid or incorrect method calls.

3. Final Answer:

   val zipped = listA.zip(listB) -> Option C

4. Quick Check:

   Use listA.zip(listB) to zip two lists [OK]

Hint: Use listA.zip(listB) to combine two lists [OK]

Common Mistakes:

• Trying to call zip as a standalone function
• Using incorrect method names like zipWith
• Concatenating lists instead of zipping

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

val nums = listOf(1, 2, 3)
val chars = listOf('a', 'b')
val zipped = nums.zip(chars)
println(zipped)

medium

A. [(1, a), (2, b), (3, null)]

B. [(a, 1), (b, 2)]

C. [(1, a), (2, b), (3, c)]

D. [(1, a), (2, b)]

Solution

1. Step 1: Identify the input lists and their lengths

   nums has 3 elements, chars has 2 elements.

2. Step 2: Understand zip output length and pairing

   Zip pairs elements by index until the shorter list ends, so only first 2 pairs: (1, 'a') and (2, 'b').

3. Final Answer:

   [(1, a), (2, b)] -> Option D

4. Quick Check:

   Zip length = shorter list length = 2 [OK]

Hint: Zip stops at shorter list length, pairs elements by index [OK]

Common Mistakes:

• Expecting zip to fill missing elements with null
• Assuming zip pairs all elements ignoring length
• Mixing order of elements in pairs

4. The following Kotlin code throws an error. What is the problem?

val list1 = listOf(1, 2, 3)
val list2 = listOf("a", "b", "c")
val zipped = list1.zip(list2) { a, b -> a + b }
println(zipped)

medium

A. Cannot add Int and String directly with + operator.

B. zip requires lists to be the same size.

C. The lambda syntax for zip is incorrect.

D. listOf cannot contain different types.

Solution

1. Step 1: Analyze the lambda inside zip

   The lambda tries to add a (Int) and b (String) using +.

2. Step 2: Understand Kotlin type rules

   Adding Int and String directly with + is not allowed; it causes a type error.

3. Final Answer:

   Cannot add Int and String directly with + operator. -> Option A

4. Quick Check:

   Int + String causes type error in Kotlin [OK]

Hint: Int + String needs explicit conversion or concatenation [OK]

Common Mistakes:

• Assuming zip needs equal list sizes
• Thinking lambda syntax is wrong
• Believing listOf can't hold different types

5. Given two lists val names = listOf("Anna", "Bob", "Cara") and val scores = listOf(90, 85), how can you create a list of strings like ["Anna: 90", "Bob: 85"] using zip with a lambda?

hard

A. names.zip(scores) { name, score -> "$name: $score" }

B. names.zip(scores).map { name, score -> "$name: $score" }

C. names.zipWith(scores) { name, score -> "$name: $score" }

D. names.zip(scores).toString { "$name: $score" }

Solution

1. Step 1: Use zip with a transform lambda

   The zip function can take a lambda to transform pairs directly into desired output.

2. Step 2: Format each pair as a string

   Using { name, score -> "$name: $score" } creates the string format needed.

3. Final Answer:

   names.zip(scores) { name, score -> "$name: $score" } -> Option A

4. Quick Check:

   Use zip with lambda to transform pairs [OK]

Hint: Use zip with lambda to format pairs directly [OK]

Common Mistakes:

• Using zipWith which doesn't exist in Kotlin
• Trying to call toString with a lambda
• Mapping after zip instead of using lambda inside zip