Spaceship operator (<=>) in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to compare two numbers using the spaceship operator.

Ruby

result = 5 [1] 3

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

A<=>

B==

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of the spaceship operator.

Using > or < which only return boolean values.

The spaceship operator <=> compares two values and returns -1, 0, or 1.

2fill in blank

medium

Complete the code to compare two strings alphabetically using the spaceship operator.

Ruby

result = 'apple' [1] 'banana'

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

A<

B==

C>=

D<=>

Attempts:

3 left

💡 Hint

Common Mistakes

Using == which only checks equality.

Using < which returns boolean, not -1, 0, or 1.

The spaceship operator compares strings lexicographically and returns -1, 0, or 1.

3fill in blank

hard

Fix the error in the code by replacing the incorrect operator with the spaceship operator.

Ruby

result = 10 [1] 10

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

A==

B<=>

C=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using == which returns boolean true or false.

Using = which is assignment, not comparison.

The spaceship operator <=> correctly compares two values and returns 0 when they are equal.

4fill in blank

hard

Fill both blanks to create a hash that maps numbers to their comparison results with 7 using the spaceship operator.

Ruby

comparisons = Hash[[5, 7, 9].map { |num| [num, num [1] 7] if num [2] 7 }.compact]

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

A<=>

B==

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of <=> in the hash values.

Using == or <=> in the filter condition incorrectly.

The first blank uses the spaceship operator to compare num with 7. The second blank filters numbers greater than 7.

5fill in blank

hard

Fill all three blanks to create a hash that maps words to their length comparison with 4 using the spaceship operator and a condition.

Ruby

result = Hash[['cat', 'house', 'dog'].map { |word| [word, word.length [1] 4] if word.length [2] 4 and word [3] 'dog' }.compact]

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

A<=>

B>

C!=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of <=> for length comparison.

Using == instead of != to exclude 'dog'.

The first blank uses the spaceship operator to compare lengths. The second blank filters words longer than 4. The third blank excludes the word 'dog'.

Practice

1.

What does the Ruby spaceship operator <=> return when comparing two values?

easy

A. true if left is smaller, false if equal, nil if left is bigger

B. -1 if left is smaller, 0 if equal, 1 if left is bigger

C. The sum of both values

D. A boolean indicating if values are equal

Solution

1. Step 1: Understand the spaceship operator purpose

   The spaceship operator compares two values and returns an integer indicating their order.

2. Step 2: Recall the return values

   It returns -1 if the left value is smaller, 0 if both are equal, and 1 if the left is bigger.

3. Final Answer:

   -1 if left is smaller, 0 if equal, 1 if left is bigger -> Option B

4. Quick Check:

   Spaceship operator returns -1, 0, or 1 [OK]

Hint: Remember: -1 smaller, 0 equal, 1 bigger [OK]

Common Mistakes:

• Confusing return values with booleans
• Thinking it returns a sum or boolean
• Mixing up which side is compared

2.

Which of the following is the correct syntax to compare a and b using the spaceship operator in Ruby?

?

easy

A. a => b

B. a =< b

C. a <= b

D. a <=> b

Solution

1. Step 1: Identify the spaceship operator syntax

   The spaceship operator is written as <=> between two values.

2. Step 2: Match the correct syntax

   Only a <=> b uses the correct operator symbol and order.

3. Final Answer:

   a <=> b -> Option D

4. Quick Check:

   Correct operator is <=> [OK]

Hint: Look for <=> exactly between variables [OK]

Common Mistakes:

• Using => which is a hash rocket
• Using <= or =< which are comparison operators
• Swapping operator symbols incorrectly

3.

What is the output of the following Ruby code?

puts 5 <=> 10
puts 10 <=> 10
puts 15 <=> 10

medium

A. false
true
false

B. 1
0
-1

C. -1
0
1

D. 10
10
10

Solution

1. Step 1: Evaluate each comparison

   5 <=> 10 returns -1 because 5 is smaller than 10.
   10 <=> 10 returns 0 because both are equal.
   15 <=> 10 returns 1 because 15 is bigger than 10.

2. Step 2: Confirm output lines

   Each puts prints the result on a new line, so output is three lines: -1, 0, 1.

3. Final Answer:

   -1 0 1 -> Option C

4. Quick Check:

   5 < 10 = -1, equal = 0, 15 > 10 = 1 [OK]

Hint: Remember: smaller = -1, equal = 0, bigger = 1 [OK]

Common Mistakes:

• Mixing up the order of output
• Expecting boolean true/false instead of -1,0,1
• Confusing <=> with < or > operators

4.

Identify the error in this Ruby code snippet using the spaceship operator:

result = 7 <=>
3
puts result

medium

A. Syntax error due to line break in operator

B. Returns nil because 7 and 3 are not comparable

C. Returns 1 as expected

D. Runtime error due to undefined variable

Solution

1. Step 1: Check operator usage across lines

   The spaceship operator <=> must be on the same line between operands; splitting it causes syntax error.

2. Step 2: Understand Ruby syntax rules

   Ruby does not allow breaking operators across lines without proper continuation, so this code raises a syntax error.

3. Final Answer:

   Syntax error due to line break in operator -> Option A

4. Quick Check:

   Operators must not be split across lines [OK]

Hint: Keep <=> on one line between values [OK]

Common Mistakes:

• Splitting operator across lines
• Assuming nil return for invalid syntax
• Confusing runtime errors with syntax errors

5.

Given the array arr = [3, 1, 4, 1, 5], which code snippet correctly sorts the array in descending order using the spaceship operator?

hard

A. arr.sort { |a, b| b <=> a }

B. arr.sort { |a, b| a == b }

C. arr.sort_by { |x| x <=> 0 }

D. arr.sort { |a, b| a <=> b }

Solution

1. Step 1: Understand sorting with spaceship operator

   The block compares two elements a and b. To sort descending, compare b to a.

2. Step 2: Analyze each option

   arr.sort { |a, b| a <=> b } sorts ascending (a <=> b).
   arr.sort { |a, b| b <=> a } sorts descending (b <=> a).
   arr.sort_by { |x| x <=> 0 } misuses sort_by with spaceship operator.
   arr.sort { |a, b| a == b } returns boolean, invalid for sorting.

3. Final Answer:

   arr.sort { |a, b| b <=> a } -> Option A

4. Quick Check:

   Reverse order uses b <=> a [OK]

Hint: Reverse order: swap a and b in <=> [OK]

Common Mistakes:

• Using a <=> b for descending sort
• Misusing sort_by with spaceship operator
• Returning boolean instead of integer in block