The reduce method looks really similar to the JavaScript one, iterates over all the elements in an Array and return a single value based on the operation we do on them.

The easiest form of this method is the sum of many numbers but in Ruby we have the ability to make our code even shorter.

nums = [1, 2, 3, 4]

sum = nums.reduce(0) { |sum, n| sum + n }

p sum # 10

In the example above, we used the long form of reduce where you set the initial value as a method parameter and you use two block parameters for the accumulation variable and the one that represents the current element.

But reduce can be written in a shorter way:

sum = nums.reduce(:+)

First and foremost we do not assign an initial value because if omitted the reduce method will automatically use the first value in the array as initial but we also do some more magic here.

We have dropped the block altogether and used the operator that we want to execute for each item as a method parameter.

Note: In this case we used an operator but it'll be valid to use even any kind of method that you can use with the object you are iterating in.

As you can see the reduce method have great potential and we can use it to simplify our code.

Resources

Those notes are taken while following the Ruby Blocks course at Pragmatic Studio.