The map Method in Ruby

The map method is one of Ruby’s most popular enumerable methods. It’s used to transform an array into another one.

Example Codes:

numbers = [2, 4, 6]

doubles = numbers.map do |n|
  n * 2
end

puts doubles

Output:

[4, 8, 12]

The above code maps through the numbers array, multiply each element by two, and produce a new doubles array. This is how the map method works.

Note that there is also a collect method, an alias to map, and both work similarly. We can show that by rewriting the above code using the collect method.

Example Codes:

numbers = [2, 4, 6]

doubles = numbers.collect do |n|
  n * 2
end

puts doubles

Output:

[4, 8, 12]

Although the map method produces a new array, there’s also a map! which works the same way as map but also mutates the original array.

Example Codes:

numbers = [2, 4, 6]

doubles = numbers.map! do |n|
  n * 2
end

puts doubles
puts numbers

Output:

[4, 8, 12]
[4, 8, 12]

Looking at the output above, you would notice that the original numbers array has been mutated and now has the same value as doubles.