 Array grouping is an extremely common operation. Seen most often when we use sequence group by clause and map reduce programming, which is better thought of as map group reduce. The ability to combine data into groups allows developers to compute higher order data sets, like the average age of a cohort or daily LCP values for a webpage. Array grouping enables these scenarios by adding the object.groupby and map.groupby static methods. Group by clause are provided callback function once for each element in an iterable. The callback function should return a string or symbol that indicates the group of the associated element. In the example on the screen, we have an array of products and we use the group by method to get them grouped by their type.