Going all the way down to the basics for Map and Reduce. Map is a function which “transforms” items in some kind of list to another kind of item and put them back in the same kind of list. suppose I have a list of numbers: [1,2,3] and I want to double every number, in … Read more
Map reduce is a framework that was developed to process massive amounts of data efficiently. For example, if we have 1 million records in a dataset, and it is stored in a relational representation – it is very expensive to derive values and perform any sort of transformations on these. For Example In SQL, Given … Read more
Linq equivalents of Map and Reduce: If you’re lucky enough to have linq then you don’t need to write your own map and reduce functions. C# 3.5 and Linq already has it albeit under different names. Map is Select: Enumerable.Range(1, 10).Select(x => x + 2); Reduce is Aggregate: Enumerable.Range(1, 10).Aggregate(0, (acc, x) => acc + … Read more
Map<String, String> x; Map<String, Integer> y = x.entrySet().stream() .collect(Collectors.toMap( e -> e.getKey(), e -> Integer.parseInt(e.getValue()) )); It’s not quite as nice as the list code. You can’t construct new Map.Entrys in a map() call so the work is mixed into the collect() call.