Zip for combining sequences in Swift - Step-by-Step Execution

Concept Flow - Zip for combining sequences

Start with two sequences

↓

Pair elements one by one

↓

Stop when shortest sequence ends

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Output pairs as combined sequence

Zip takes two sequences and pairs their elements one by one until the shortest sequence ends.

Execution Sample

Swift

let numbers = [1, 2, 3]
let letters = ["a", "b", "c", "d"]
for pair in zip(numbers, letters) {
    print(pair)
}

This code pairs elements from two arrays and prints each pair.

Execution Table

Iteration	numbers element	letters element	Pair formed	Output
1	1	"a"	(1, "a")	(1, "a")
2	2	"b"	(2, "b")	(2, "b")
3	3	"c"	(3, "c")	(3, "c")
4	-	"d"	-	Stop: shortest sequence ended

💡 Stops after 3 iterations because numbers has only 3 elements.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
numbers element	-	1	2	3	-
letters element	-	"a"	"b"	"c"	-
pair	-	(1, "a")	(2, "b")	(3, "c")	-

Key Moments - 2 Insights

Why does the loop stop before reaching the last element "d" in letters?

Zip stops when the shortest sequence ends, so since numbers has 3 elements, the loop stops after 3 pairs (see execution_table row 4).

What type of value is 'pair' inside the loop?

Each 'pair' is a tuple combining one element from numbers and one from letters, shown in execution_table under 'Pair formed'.

Visual Quiz - 3 Questions

Look at the execution_table, what is the pair formed at iteration 2?

A (2, "a")

B (1, "b")

C (2, "b")

D (3, "c")

💡 Hint

Check the 'Pair formed' column at iteration 2 in the execution_table.

At which iteration does the zip stop pairing elements?

A After iteration 2

B After iteration 3

C After iteration 4

D After iteration 1

💡 Hint

Look at the exit_note and the last row in execution_table.

If numbers had 5 elements instead of 3, how would the zip behave?

A It would pair 4 elements and stop

B It would pair 3 elements and stop

C It would pair 5 elements and stop

D It would pair 6 elements and stop

💡 Hint

Zip stops at the shortest sequence length; letters has 4 elements (see concept_flow).

Concept Snapshot

Zip combines two sequences element-wise into pairs.
Stops when the shortest sequence ends.
Syntax: zip(seq1, seq2)
Returns sequence of tuples.
Useful to process two lists together.

Full Transcript

Zip in Swift takes two sequences and pairs their elements one by one until the shortest sequence ends. For example, given numbers = [1, 2, 3] and letters = ["a", "b", "c", "d"], zip(numbers, letters) pairs (1, "a"), (2, "b"), and (3, "c") and stops before "d" because numbers has only 3 elements. Each pair is a tuple combining one element from each sequence. This is useful to process two lists together safely without running out of elements.