When I began to study Ruby, it was a little confusing for me to distinguish each and map . I even read articles about it more than one time. Using them in different situations helped me understand better, and I’d hope I can explain them to someone that is confused as I was.

The main difference that you can find in any article about it is that each iterates over a collection of values, NOT changing the origin array. So, it’s easy to think that map not only iterates over a collection of values but also returns a new array containing the return of each iteration.

Example:

array = [2, 4, 6, 8]
array.each { |element| element / 2 }
#=> [2, 4, 6, 8] 
array = [2, 4, 6, 8]
array.map { |element| element / 2 }
#=> [1, 2, 3, 4]

However, I kept asking myself WHEN is better to use ‘each’. I realized that sometimes you’re not concerned about the iteration return and don’t want to allocate memory for it, so in these cases is better to use each.

Array documentation