Find/detect for first match in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the find method do in Ruby?

The find method returns the first element in a collection that matches a given condition. If no element matches, it returns nil.

beginner

How is detect related to find in Ruby?

In Ruby, detect is an alias for find. Both methods do exactly the same thing: return the first matching element.

beginner

What will [1, 2, 3, 4].find { |n| n > 2 } return?

It will return 3, because 3 is the first number in the array greater than 2.

beginner

What happens if no element matches the condition in find?

If no element matches, find returns nil.

intermediate

Can find be used on hashes in Ruby?

Yes, find can be used on hashes. It returns the first key-value pair (as a two-element array) that matches the condition.

What does find return if no element matches the condition?

A nil

B An empty array

C An error

D The whole collection

If no element matches, find returns nil.

Which method is an alias for find in Ruby?

A select

B detect

C map

D each

detect is an alias for find in Ruby.

What will [10, 20, 30].find { |x| x < 15 } return?

A 20

B 30

C nil

D 10

10 is the first element less than 15, so it is returned.

Can find be used on a hash to find a key-value pair?

A No, it raises an error

B No, it only works on arrays

C Yes, it returns the first matching pair as an array

D Yes, but it returns only the key

find works on hashes and returns the first matching key-value pair as an array.

What is the difference between find and select?

A <code>find</code> returns first match, <code>select</code> returns all matches

B <code>find</code> returns all matches, <code>select</code> returns first match

C They are the same

D <code>select</code> returns nil if no match, <code>find</code> raises error

find returns the first matching element, while select returns all matching elements.

Explain how the find method works in Ruby and give an example.

Think about searching for the first item that fits a rule.

Describe the relationship between find and detect in Ruby.

They are two names for the same method.