Merge and update methods in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to merge two hashes using the merge method.

Ruby

hash1 = {a: 1, b: 2}
hash2 = {b: 3, c: 4}
result = hash1.[1](hash2)
puts result

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

Aupdate

Bcombine

Cmerge

Dconcat

Attempts:

3 left

💡 Hint

Common Mistakes

Using update instead of merge changes the original hash.

The merge method combines two hashes and returns a new hash without modifying the original.

2fill in blank

medium

Complete the code to update a hash with another hash using the update method.

Ruby

hash1 = {x: 10, y: 20}
hash2 = {y: 30, z: 40}
hash1.[1](hash2)
puts hash1

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

Aupdate

Bmerge

Creplace

Dconcat

Attempts:

3 left

💡 Hint

Common Mistakes

Using merge instead of update does not change the original hash.

The update method modifies the original hash by adding or replacing keys from another hash.

3fill in blank

hard

Fix the error in the code to correctly merge two hashes with a block to handle conflicts.

Ruby

h1 = {a: 100, b: 200}
h2 = {b: 254, c: 300}
result = h1.merge(h2) { |key, old_val, new_val| [1] }
puts result

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

Aold_val * new_val

Bold_val - new_val

Cnew_val - old_val

Dold_val + new_val

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication changes the intended result.

The block tells merge how to combine values when keys overlap. Here, it adds the old and new values.

4fill in blank

hard

Fill both blanks to create a hash comprehension that merges two hashes and keeps the larger value for duplicate keys.

Ruby

h1 = {a: 5, b: 10}
h2 = {b: 7, c: 12}
result = h1.merge(h2) { |[1], old_val, new_val| old_val [2] new_val ? old_val : new_val }
puts result

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

Akey

Bk

Cx

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names or comparison operators.

The block compares old and new values and keeps the larger one. The first blank is the block variable for the key, usually key. The second blank is the comparison operator >.

5fill in blank

hard

Fill all three blanks to update a hash with another hash, but keep the original value if the new value is nil.

Ruby

h1 = {a: 1, b: 2}
h2 = {b: nil, c: 3}
h1.update(h2) { |[1], old_val, new_val| new_val [2] nil ? new_val : [3] }
puts h1

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

Akey

B!=

Cold_val

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of != causes wrong logic.

Returning new_val when it is nil replaces original value incorrectly.

The block checks if the new value is not nil. If so, it uses the new value; otherwise, it keeps the old value. The first blank is the block variable for the key, usually key. The second blank is the not equal operator !=. The third blank is old_val to keep the original value.

Practice

1.

Which Ruby method returns a new hash by combining two hashes without changing the original?

easy

A. merge

B. merge!

C. update

D. replace

Solution

1. Step 1: Understand merge behavior

   merge returns a new hash combining two hashes without modifying the original.

2. Step 2: Compare with merge! and update

   Both merge! and update modify the original hash, so they don't return a new one.

3. Final Answer:

   merge -> Option A

4. Quick Check:

   merge returns new hash [OK]

Hint: Remember: merge returns new hash, merge! updates original [OK]

Common Mistakes:

• Confusing merge and merge! methods
• Thinking update returns a new hash
• Assuming replace merges hashes

2.

Which of the following is the correct syntax to update hash a with hash b in Ruby?

a = {x: 1}

b = {y: 2}

easy

A. a + b

B. a.merge!b

C. a.merge b

D. a.update(b)

Solution

1. Step 1: Check syntax for updating hash

   update is a method that modifies the original hash and takes another hash as argument with parentheses.

2. Step 2: Compare with other options

   merge! also updates but usually called with ! and parentheses are optional but update(b) is the most explicit and correct syntax here.

3. Final Answer:

   a.update(b) -> Option D

4. Quick Check:

   Use update() to modify original hash [OK]

Hint: Use update(hash) to change original hash [OK]

Common Mistakes:

• Using + operator to combine hashes (not valid)
• Forgetting parentheses in method call
• Confusing merge and update syntax

3.

What is the output of this Ruby code?

a = {a: 1, b: 2}

b = {b: 3, c: 4}

c = a.merge(b)

puts c

medium

A. {:a=>1, :b=>2, :c=>4}

B. {:a=>1, :b=>3}

C. {:a=>1, :b=>3, :c=>4}

D. {:b=>3, :c=>4}

Solution

1. Step 1: Understand merge behavior with overlapping keys

   merge returns a new hash combining keys; overlapping keys get values from the second hash.

2. Step 2: Apply to given hashes

   Key :b is in both hashes; value from b (3) replaces value from a (2). Keys :a and :c are included as is.

3. Final Answer:

   {:a=>1, :b=>3, :c=>4} -> Option C

4. Quick Check:

   Overlapping keys replaced by second hash [OK]

Hint: Overlapping keys take second hash's value in merge [OK]

Common Mistakes:

• Assuming original hash is changed by merge
• Not replacing overlapping key values
• Missing keys from either hash

4.

Identify the error in this Ruby code snippet:

a = {x: 10}

b = {y: 20}

a.merge! b

puts a

medium

A. Output will be empty hash

B. No error; code works correctly

C. Runtime error because merge! cannot be used with variables

D. Syntax error due to missing parentheses in merge!

Solution

1. Step 1: Check syntax of merge! method call

   merge! can be called without parentheses in Ruby, so a.merge! b is valid syntax.

2. Step 2: Verify runtime behavior

   merge! updates a with keys and values from b, so a becomes {x: 10, y: 20}. No errors occur.

3. Final Answer:

   No error; code works correctly -> Option B

4. Quick Check:

   merge! updates original hash without error [OK]

Hint: merge! can be called without parentheses [OK]

Common Mistakes:

• Thinking parentheses are mandatory
• Assuming merge! returns a new hash
• Expecting runtime error with variable argument

5.

You have two hashes:

h1 = {a: 1, b: 2, c: 3}

h2 = {b: 20, d: 4}

You want to update h1 with h2 but only keep keys from h2 that have values greater than 10. Which code correctly does this?

hard

A. h1.update(h2.select { |k, v| v > 10 })

B. h1.update(h2.reject { |k, v| v > 10 })

C. h1.merge(h2.select { |k, v| v > 10 })

D. h1.replace(h2.select { |k, v| v > 10 })

Solution

1. Step 1: Filter h2 keys with values > 10

   Use select { |k, v| v > 10 } to keep only keys with values greater than 10.

2. Step 2: Update h1 with filtered h2

   Use update to modify h1 in place with the filtered hash.

3. Step 3: Check other options

   merge! also updates but update is clearer; merge returns new hash and does not modify h1.

4. Final Answer:

   h1.update(h2.select { |k, v| v > 10 }) -> Option A

5. Quick Check:

   Filter then update original hash [OK]

Hint: Filter with select, then update original hash [OK]

Common Mistakes:

• Using merge instead of update (does not modify original)
• Not filtering keys before update
• Using reject incorrectly