This is interesting to me because the map reduce has way less cognitive load for me.

With map reduce I see the following:

- We've got an array

- We're going to loop through it and square everything

- We're going to take that and add it all together

- The result is r

When I read the for-loop counterpart:

- We have a variable called r that we're initializing to 0

- We're starting a loop with j as the index initialized to 0 iterating through an array

- We've got a variable x on each iteration that is the current position in the array

- We're adding the square of x to r

Maybe it's a personal quirk. for-loops make me feel stupid.