Hash methods (keys, values, each) in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get all keys from the hash.

Ruby

my_hash = {a: 1, b: 2, c: 3}
keys = my_hash.[1]
puts keys

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

Akeys

Bvalues

Ceach

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'values' instead of 'keys' returns the values, not keys.

Using 'each' returns an enumerator, not an array of keys.

The keys method returns an array of all keys in the hash.

2fill in blank

medium

Complete the code to get all values from the hash.

Ruby

my_hash = {x: 10, y: 20, z: 30}
vals = my_hash.[1]
puts vals

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

Akeys

Bvalues

Ceach_key

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'keys' returns keys, not values.

Using 'each_key' returns an enumerator for keys, not values.

The values method returns an array of all values in the hash.

3fill in blank

hard

Fix the error in the code to print each key and value pair.

Ruby

my_hash = {name: 'Alice', age: 30}
my_hash.[1] do |key, value|
  puts "#{key}: #{value}"
end

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

Akeys

Bvalues

Ceach

Dmap

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'keys' or 'values' returns arrays, not pairs.

Using 'map' returns a new array, not just iteration.

The each method iterates over each key-value pair in the hash.

4fill in blank

hard

Fill both blanks to create a hash of word lengths for words longer than 3 letters.

Ruby

words = ['cat', 'house', 'tree', 'a', 'dog']
lengths = {}
words.each do |word|
  if word.length [2] 3
    lengths[word] = word[1]
  end
end
puts lengths

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

A.length

B>

C<

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' filters shorter words.

Forgetting to use '.length' to get word length.

Use .length to get the length of each word and > to filter words longer than 3 letters.

5fill in blank

hard

Fill all three blanks to create a hash with uppercase keys and values greater than 10.

Ruby

data = {"a": 5, "b": 15, "c": 25}
result = {}
data.[3] do |k, v|
  if v > 10
    result[[1]] = [2]
  end
end
puts result

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

Ak.upcase

Bv

Ceach

Dk

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'k' instead of 'k.upcase' keeps keys lowercase.

Using 'map' instead of 'each' changes the return type.

Use each to iterate, k.upcase for uppercase keys, and v for values.

Practice

1. What does the keys method do when called on a Ruby hash?

easy

A. Deletes all keys from the hash

B. Returns an array of all the values in the hash

C. Returns an array of all the keys in the hash

D. Iterates over each key-value pair in the hash

Solution

1. Step 1: Understand the keys method

   The keys method extracts all keys from the hash and returns them as an array.

2. Step 2: Compare with other methods

   values returns values, each iterates pairs, so only keys returns keys array.

3. Final Answer:

   Returns an array of all the keys in the hash -> Option C

4. Quick Check:

   keys = keys array [OK]

Hint: Remember: keys method lists all keys as an array [OK]

Common Mistakes:

• Confusing keys with values method
• Thinking keys modifies the hash
• Mixing up keys with each method

2. Which of the following is the correct syntax to iterate over each key-value pair in a Ruby hash h?

easy

A. h.each(key, value) { puts key, value }

B. h.each { |key, value| puts key + value }

C. h.each do |key value| puts key, value end

D. h.each { key, value -> puts key + value }

Solution

1. Step 1: Identify correct block syntax for each

   The correct syntax uses curly braces or do-end with block parameters separated by a comma inside pipes: { |key, value| ... }.

2. Step 2: Check each option

   h.each { |key, value| puts key + value } uses correct syntax with pipes and comma. Others have syntax errors or wrong block format.

3. Final Answer:

   h.each { |key, value| puts key + value } -> Option B

4. Quick Check:

   Correct block syntax = h.each { |key, value| puts key + value } [OK]

Hint: Use pipes and commas inside block for key-value pairs [OK]

Common Mistakes:

• Omitting pipes around block parameters
• Missing comma between key and value
• Using arrow syntax incorrectly in blocks

3. What will be the output of the following Ruby code?

h = {a: 1, b: 2, c: 3}
h.keys

medium

A. [:1, :2, :3]

B. [1, 2, 3]

C. {a: 1, b: 2, c: 3}

D. [:a, :b, :c]

Solution

1. Step 1: Understand keys method on hash

   The keys method returns an array of all keys in the hash. Here keys are symbols :a, :b, :c.

2. Step 2: Match output with options

   [:a, :b, :c] matches the array of keys. [1, 2, 3] is values, C is the whole hash, D is invalid symbol array.

3. Final Answer:

   [:a, :b, :c] -> Option D

4. Quick Check:

   h.keys = [:a, :b, :c] [OK]

Hint: keys returns array of keys exactly as in hash [OK]

Common Mistakes:

• Confusing keys with values output
• Expecting hash instead of array
• Misreading symbols as strings

4. Identify the error in the following Ruby code snippet:

h = {x: 10, y: 20}
h.each do |k v|
  puts "#{k}: #{v}"
end

medium

A. Missing comma between block parameters k and v

B. Hash keys must be strings, not symbols

C. The each method cannot be used with do-end

D. The puts statement syntax is incorrect

Solution

1. Step 1: Check block parameter syntax

   Block parameters must be separated by a comma inside pipes: |k, v|. Here comma is missing.

2. Step 2: Verify other parts

   Keys as symbols are valid, each do-end is valid, and puts syntax is correct.

3. Final Answer:

   Missing comma between block parameters k and v -> Option A

4. Quick Check:

   Block params need comma [OK]

Hint: Always separate block parameters with commas inside pipes [OK]

Common Mistakes:

• Omitting comma between block variables
• Thinking symbols are invalid keys
• Confusing block syntax with method call

5. Given the hash h = {a: 1, b: 0, c: nil, d: 4}, which code snippet correctly returns an array of keys whose values are truthy (not false or nil)?

hard

A. h.select { |k, v| v }.keys

B. h.keys.select { |k| k }

C. h.values.select { |v| v }.keys

D. h.each { |k, v| k if v }.keys

Solution

1. Step 1: Understand filtering keys by truthy values

   We want keys where values are truthy (not false or nil). select filters pairs by value truthiness.

2. Step 2: Analyze each option

   h.select { |k, v| v }.keys filters hash pairs by truthy value, then gets keys -> [:a, :d] [check]. h.keys.select { |k| k } checks if key truthy (all symbols are), returns all keys. h.values.select { |v| v }.keys calls keys on array (NoMethodError). h.each { |k, v| k if v }.keys returns original hash, no filtering.

3. Final Answer:

   h.select { |k, v| v }.keys -> Option A

4. Quick Check:

   Filter pairs then get keys = h.select { |k, v| v }.keys [OK]

Hint: Use select on hash then call keys to filter by values [OK]

Common Mistakes:

• Trying to call keys on array of values
• Using each instead of select for filtering
• Selecting keys without checking values