Here is a fun summary by Steven Luscher: Map/filter/reduce in a tweet: Array iteration will generally not be your performance bottleneck. The analysis uses basic operations and heavy data manipulation to analyze the execution speed of each method. We have for of loops for reduce and loop tests and "plain-old simple for loops" for simple reduce and simple loop tests. Here is a fun summary by Steven Luscher: Map/filter/reduce in a tweet: This caused me to wonder what was the programmatic difference between reduce and a traditional for-loop? reduce, on the other hand, takes all of the elements in an array and reduces them into a single value. link brightness_4 code