Zip operation in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Zip operation?

Consider the following C# code using Zip to combine two arrays. What will be printed?

C Sharp (C#)

var numbers = new[] {1, 2, 3};
var words = new[] {"one", "two", "three"};
var zipped = numbers.Zip(words, (n, w) => $"{n}-{w}");
foreach (var item in zipped) {
    Console.WriteLine(item);
}

A one-1\ntwo-2\nthree-3

B 1\n2\n3\none\ntwo\nthree

C Compilation error

D 1-one\n2-two\n3-three

💡 Hint

Zip pairs elements from two sequences in order.

The Zip method pairs elements from the first and second arrays by index, then applies the lambda to create strings like "1-one".

❓ Predict Output

intermediate

What is the output when sequences have different lengths?

What will this C# code print when using Zip on arrays of different lengths?

C Sharp (C#)

var a = new[] {10, 20, 30, 40};
var b = new[] {"a", "b"};
var zipped = a.Zip(b, (x, y) => $"{x}{y}");
foreach (var s in zipped) Console.WriteLine(s);

A Runtime exception

B 10a\n20b

C 10a\n20b\n30b\n40b

D 10a\n20b\n30\n40

💡 Hint

Zip stops at the shortest sequence length.

Zip pairs elements until one sequence runs out. Here, only first two pairs are zipped.

🔧 Debug

advanced

What error does this Zip code cause?

What error will this C# code produce when run?

C Sharp (C#)

var list1 = new List<int> {1, 2, 3};
List<string> list2 = null;
var zipped = list1.Zip(list2, (x, y) => x + y.Length);
foreach (var item in zipped) Console.WriteLine(item);

A NullReferenceException

B ArgumentNullException

C No error, prints 3 lines

D Compilation error

💡 Hint

Check what happens if one sequence is null.

Calling Zip with a null second sequence causes a NullReferenceException at runtime.

❓ Predict Output

advanced

What is the output of this Zip with index?

What will this C# code print?

C Sharp (C#)

var nums = new[] {5, 10, 15};
var words = new[] {"five", "ten", "fifteen"};
var zipped = nums.Zip(words, (n, w) => $"{w}:{n}");
var indexed = zipped.Select((s, i) => $"{i}-{s}");
foreach (var item in indexed) Console.WriteLine(item);

A 0-five:5\n1-ten:10\n2-fifteen:15

B Compilation error

C 5-five\n10-ten\n15-fifteen

D five:5\nten:10\nfifteen:15

💡 Hint

Select with index adds the position before each string.

Zip pairs elements, then Select adds the index before each pair string.

🧠 Conceptual

expert

How many items are in the result of this Zip?

Given these sequences, how many items will the Zip produce?

C Sharp (C#)

var seq1 = Enumerable.Range(1, 100);
var seq2 = Enumerable.Range(1, 50);
var result = seq1.Zip(seq2, (x, y) => x + y);

A 150

B 100

C 50

D 0

💡 Hint

Zip stops at the shortest sequence length.

Zip produces as many items as the shortest input sequence length, which is 50 here.

Practice

1.

What does the Zip method do in C#?

Choose the best description.

easy

A. Combines all elements from two collections into one long list.

B. Sorts elements in a collection in ascending order.

C. Filters elements from a collection based on a condition.

D. Pairs elements from two collections one by one until the shorter ends.

Solution

1. Step 1: Understand the purpose of Zip

   The Zip method pairs elements from two collections by their positions.

2. Step 2: Recognize stopping condition

   It stops when the shorter collection runs out of elements, so no extra elements are included.

3. Final Answer:

   Pairs elements from two collections one by one until the shorter ends. -> Option D

4. Quick Check:

   Zip pairs elements until the shorter ends = B [OK]

Hint: Zip pairs elements until shortest collection ends [OK]

Common Mistakes:

• Thinking Zip combines all elements regardless of length
• Confusing Zip with filtering or sorting
• Assuming Zip merges collections end-to-end

2.

Which of the following is the correct syntax to use Zip on two lists list1 and list2 to sum their elements?

var result = list1.Zip(list2, (a, b) => ? );

easy

A. a + b

B. a - b

C. a * b

D. a / b

Solution

1. Step 1: Identify the operation to sum elements

   The lambda expression should add the two elements: a + b.

2. Step 2: Confirm syntax correctness

   The syntax list1.Zip(list2, (a, b) => a + b) correctly sums paired elements.

3. Final Answer:

   a + b -> Option A

4. Quick Check:

   Sum elements with Zip = a + b [OK]

Hint: Use (a, b) => a + b to sum zipped elements [OK]

Common Mistakes:

• Using wrong operator like - or * instead of +
• Forgetting lambda syntax
• Mixing parameter order

3.

What is the output of this C# code?

var numbers = new[] {1, 2, 3};
var words = new[] {"one", "two"};
var zipped = numbers.Zip(words, (n, w) => $"{n}:{w}");
foreach(var item in zipped) Console.Write(item + " ");

medium

A. 1:one 2:two 3:

B. one:1 two:2

C. 1:one 2:two

D. 1:one 2:two 3:three

Solution

1. Step 1: Check lengths of arrays

   numbers has 3 elements, words has 2 elements; Zip stops at shorter length (2).

2. Step 2: Pair elements and format output

   Pairs: (1, "one"), (2, "two"); output strings: "1:one", "2:two".

3. Final Answer:

   1:one 2:two -> Option C

4. Quick Check:

   Zip stops at shorter list = C [OK]

Hint: Zip stops at shorter list length, so output matches shortest [OK]

Common Mistakes:

• Expecting output for all elements of longer list
• Mixing order of elements in output
• Adding extra spaces or elements

4.

Identify the error in this code snippet using Zip:

var a = new[] {1, 2, 3};
var b = new[] {4, 5};
var result = a.Zip(b, (x, y) => x + y).ToList();
Console.WriteLine(result[2]);

medium

A. Syntax error in Zip lambda expression

B. Index out of range exception at result[2]

C. Null reference exception

D. No error, prints 7

Solution

1. Step 1: Understand Zip output length

   Zip stops at shorter array length, so result has 2 elements only.

2. Step 2: Accessing invalid index

   Accessing result[2] (third element) causes IndexOutOfRangeException.

3. Final Answer:

   Index out of range exception at result[2] -> Option B

4. Quick Check:

   Accessing beyond Zip length causes error = A [OK]

Hint: Zip result length = shorter input length; check indexes [OK]

Common Mistakes:

• Assuming Zip output length equals longer list
• Ignoring zero-based indexing
• Confusing syntax errors with runtime errors

5.

You have two lists:

var keys = new[] {"a", "b", "c", "d"};
var values = new[] {1, 2, 3};

Using Zip, how can you create a dictionary that pairs keys and values only for matching positions?

hard

A. keys.Zip(values, (k, v) => new {k, v}).ToDictionary(x => x.k, x => x.v)

B. keys.Select((k, i) => new {k, v = values[i]}).ToDictionary(x => x.k, x => x.v)

C. keys.Concat(values).ToDictionary(k => k, v => v)

D. values.Zip(keys, (k, v) => new {k, v}).ToDictionary(x => x.k, x => x.v)

Solution

1. Step 1: Use Zip to pair keys and values

   Zip pairs elements by position, stopping at shorter list length (3 pairs).

2. Step 2: Convert pairs to dictionary

   Create anonymous objects with key and value, then call ToDictionary with key and value selectors.

3. Final Answer:

   keys.Zip(values, (k, v) => new {k, v}).ToDictionary(x => x.k, x => x.v) -> Option A

4. Quick Check:

   Zip pairs + ToDictionary = A [OK]

Hint: Zip keys and values, then ToDictionary with selectors [OK]

Common Mistakes:

• Using Concat instead of Zip
• Reversing keys and values in Zip
• Using Select without bounds check causing errors