Partition for splitting in Kotlin - Mini Project: Build & Apply

Partition for splitting

📖 Scenario: Imagine you have a list of numbers representing daily temperatures. You want to separate these temperatures into two groups: those that are warm (above a certain threshold) and those that are cool (at or below that threshold).

🎯 Goal: You will create a Kotlin program that uses the partition function to split a list of temperatures into warm and cool days.

📋 What You'll Learn

Create a list of integers called temperatures with the exact values: 15, 22, 8, 30, 18, 5

Create an integer variable called threshold and set it to 20

Use the partition function on temperatures with a condition that checks if a temperature is greater than threshold

Print the two resulting lists with the exact variable names warmDays and coolDays

💡 Why This Matters

🌍 Real World

Partitioning data helps in sorting and organizing information, like separating warm and cool days for weather reports.

💼 Career

Understanding how to split data based on conditions is useful in data analysis, software development, and creating user-friendly applications.

1

Create the list of temperatures

Create a list of integers called temperatures with these exact values: 15, 22, 8, 30, 18, 5

Kotlin

// Create the list of temperatures
// Your code here

Hint

Use listOf to create the list with the exact numbers given.

2

Set the threshold value

Create an integer variable called threshold and set it to 20

Kotlin

val temperatures = listOf(15, 22, 8, 30, 18, 5)
// Create the threshold variable
// Your code here

Hint

Use val threshold = 20 to create the variable.

3

Partition the temperatures

Use the partition function on temperatures with a condition that checks if a temperature is greater than threshold. Store the first list in warmDays and the second list in coolDays

Kotlin

val temperatures = listOf(15, 22, 8, 30, 18, 5)
val threshold = 20
// Use partition to split temperatures
// Your code here

Hint

Use val (warmDays, coolDays) = temperatures.partition { it > threshold } to split the list.

4

Print the warm and cool days

Print the lists warmDays and coolDays exactly using two separate println statements

Kotlin

val temperatures = listOf(15, 22, 8, 30, 18, 5)
val threshold = 20
val (warmDays, coolDays) = temperatures.partition { it > threshold }
// Print warmDays and coolDays
// Your code here

Hint

Use println(warmDays) and println(coolDays) to show the results.

Practice

1. What does the partition function do in Kotlin when applied to a list?

easy

A. Converts the list into a map with indices as keys.

B. Sorts the list in ascending order.

C. Removes duplicate elements from the list.

D. Splits the list into two lists based on a condition, returning a Pair of lists.

Solution

1. Step 1: Understand the purpose of partition

   The partition function divides a list into two parts based on a condition.

2. Step 2: Recognize the return type

   It returns a Pair where the first list contains elements matching the condition, and the second list contains the rest.

3. Final Answer:

   Splits the list into two lists based on a condition, returning a Pair of lists. -> Option D

4. Quick Check:

   partition = split by condition [OK]

Hint: Remember: partition always returns two lists in a Pair [OK]

Common Mistakes:

• Thinking partition sorts the list
• Confusing partition with filtering
• Assuming partition removes duplicates

2. Which of the following is the correct syntax to use partition on a list numbers to split even and odd numbers?

easy

A. val (evens, odds) = numbers.partition { it % 2 == 0 }

B. val (evens, odds) = numbers.partition(it % 2 == 0)

C. val evens = numbers.partition { it % 2 == 0 }

D. val evens, odds = numbers.partition { it % 2 == 0 }

Solution

1. Step 1: Check the lambda syntax inside partition

   The condition must be inside curly braces with it representing each element.

2. Step 2: Verify destructuring declaration

   Partition returns a Pair, so use val (first, second) = ... to get both lists.

3. Final Answer:

   val (evens, odds) = numbers.partition { it % 2 == 0 } -> Option A

4. Quick Check:

   Correct lambda and destructuring = val (evens, odds) = numbers.partition { it % 2 == 0 } [OK]

Hint: Use val (a, b) = list.partition { condition } [OK]

Common Mistakes:

• Missing curly braces for lambda
• Not using destructuring for Pair
• Using parentheses instead of braces for lambda

3. What is the output of this Kotlin code?

val words = listOf("apple", "banana", "avocado", "berry")
val (aWords, otherWords) = words.partition { it.startsWith('a') }
println(aWords)
println(otherWords)

medium

A. ["apple", "avocado"]
["banana", "berry"]

B. ["banana", "berry"]
["apple", "avocado"]

C. ["apple"]
["banana", "avocado", "berry"]

D. ["avocado"]
["apple", "banana", "berry"]

Solution

1. Step 1: Apply the condition to each word

   Check which words start with 'a': "apple" and "avocado" match.

2. Step 2: Partition splits into two lists

   First list has words starting with 'a', second list has the rest: "banana", "berry".

3. Final Answer:

   ["apple", "avocado"] ["banana", "berry"] -> Option A

4. Quick Check:

   partition by startsWith('a') = ["apple", "avocado"] ["banana", "berry"] [OK]

Hint: Check condition on each element carefully [OK]

Common Mistakes:

• Mixing order of lists in output
• Forgetting that partition returns Pair of lists
• Confusing startsWith with contains

4. Identify the error in this Kotlin code using partition:

val nums = listOf(1, 2, 3, 4)
val evens, odds = nums.partition { it % 2 == 0 }
println(evens)
println(odds)

medium

A. partition cannot be used on lists of integers.

B. The lambda condition is incorrect; should be it % 2 != 0.

C. Missing parentheses around evens and odds for destructuring declaration.

D. println statements are missing string interpolation.

Solution

1. Step 1: Check destructuring declaration syntax

   Destructuring a Pair requires parentheses: val (evens, odds) = ....

2. Step 2: Confirm lambda and usage

   The lambda is correct for evens; partition works on lists of integers; println is fine.

3. Final Answer:

   Missing parentheses around evens and odds for destructuring declaration. -> Option C

4. Quick Check:

   Destructuring needs parentheses [OK]

Hint: Use val (a, b) = ... for destructuring Pair [OK]

Common Mistakes:

• Omitting parentheses in destructuring
• Changing correct lambda unnecessarily
• Thinking partition only works on strings

5. Given a list of mixed integers including zero and negatives, how can you use partition to separate positive numbers from zero and negatives? Choose the correct code snippet.

hard

A. val (positives, nonPositives) = numbers.partition { it < 0 }

B. val (positives, nonPositives) = numbers.partition { it > 0 }

C. val (positives, nonPositives) = numbers.partition { it >= 0 }

D. val (positives, nonPositives) = numbers.partition { it == 0 }

Solution

1. Step 1: Define the condition for positives

   Positive numbers are greater than zero, so condition is it > 0.

2. Step 2: Use partition with this condition

   Partition splits list into positives and the rest (zero and negatives).

3. Final Answer:

   val (positives, nonPositives) = numbers.partition { it > 0 } -> Option B

4. Quick Check:

   Partition by it > 0 separates positives [OK]

Hint: Use it > 0 to get positives, rest are zero/negatives [OK]

Common Mistakes:

• Using it >= 0 includes zero as positive
• Using it < 0 reverses groups
• Using it == 0 only selects zeros