Zip for combining collections in Kotlin - Step-by-Step Execution

Concept Flow - Zip for combining collections

Start with two lists

↓

Take first element from each list

↓

Pair elements together

↓

Add pair to result list

↓

Move to next elements

↓

Repeat until one list ends

↓

Return list of pairs

Zip takes two collections and pairs their elements one by one until one runs out.

Execution Sample

Kotlin

val list1 = listOf("a", "b", "c")
val list2 = listOf(1, 2, 3)
val zipped = list1.zip(list2)
println(zipped)

This code pairs elements from two lists into a list of pairs.

Execution Table

Step	list1 element	list2 element	Pair created	Result list so far
1	"a"	1	("a", 1)	[("a", 1)]
2	"b"	2	("b", 2)	[("a", 1), ("b", 2)]
3	"c"	3	("c", 3)	[("a", 1), ("b", 2), ("c", 3)]
4	No more elements	No more elements	Stop	Final result: [("a", 1), ("b", 2), ("c", 3)]

💡 Stop when one list runs out of elements (both lists ended here).

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
list1 element	N/A	"a"	"b"	"c"	No more elements
list2 element	N/A	1	2	3	No more elements
Result list	[]	[("a", 1)]	[("a", 1), ("b", 2)]	[("a", 1), ("b", 2), ("c", 3)]	[("a", 1), ("b", 2), ("c", 3)]

Key Moments - 3 Insights

Why does the zip stop when one list is shorter?

Zip pairs elements only while both lists have elements. When one ends, no more pairs can be made, as shown in step 4 of the execution_table.

What happens if lists have different types of elements?

Zip can combine any types because it creates pairs of the elements as they are, like pairing a String with an Int in the example.

Does zip change the original lists?

No, zip creates a new list of pairs without modifying the original lists, as seen in variable_tracker where list1 and list2 elements remain unchanged.

Visual Quiz - 3 Questions

Look at the execution_table, what is the pair created at step 2?

A ("a", 1)

B ("b", 2)

C ("c", 3)

D ("b", 3)

💡 Hint

Check the 'Pair created' column at step 2 in the execution_table.

At which step does the zip operation stop according to the execution_table?

A Step 4

B Step 3

C Step 2

D Step 1

💡 Hint

Look for the row where 'Stop' appears in the 'Pair created' column.

If list2 had only two elements, how would the final result list change?

A It would be empty

B It would have three pairs

C It would have two pairs only

D It would have one pair

💡 Hint

Zip stops when one list ends, so result length matches shorter list length.

Concept Snapshot

Zip combines two collections element-wise.
Pairs elements until one collection ends.
Returns a list of pairs.
Original collections stay unchanged.
Useful to combine related data simply.

Full Transcript

Zip in Kotlin takes two lists and pairs their elements one by one. It starts from the first elements of both lists, creates a pair, and adds it to a new list. Then it moves to the next elements and repeats this until one list runs out of elements. The result is a list of pairs. The original lists do not change. This is useful when you want to combine two related lists into one list of pairs.