What is the difference between groupByKey and reduceByKey in Spark?

Both reduceByKey and groupByKey result in wide transformations which means both triggers a shuffle operation. The key difference between reduceByKey and groupByKey is that reduceByKey does a map side combine and groupByKey does not do a map side combine.

What is the difference between fold and reduce?

Fold and reduce The difference between the two functions is that fold() takes an initial value and uses it as the accumulated value on the first step, whereas the first step of reduce() uses the first and the second elements as operation arguments on the first step.

How does Foldbykey spark work?

Merge the values for each key using an associative function “func” and a neutral “zeroValue” which may be added to the result an arbitrary number of times, and must not change the result (e.g., 0 for addition, or 1 for multiplication.).

Why is groupByKey better than reduceByKey?

groupByKey can cause out of disk problems as data is sent over the network and collected on the reduced workers. Data are combined at each partition, with only one output for one key at each partition to send over the network. reduceByKey required combining all your values into another value with the exact same type.

What is fold in Scala?

The fold function is applicable to both Scala’s Mutable and Immutable collection data structures. The fold method takes an associative binary operator function as parameter and will use it to collapse elements from the collection. The fold method allows you to also specify an initial value.

Is reduce a fold?

In functional programming, fold (also termed reduce, accumulate, aggregate, compress, or inject) refers to a family of higher-order functions that analyze a recursive data structure and through use of a given combining operation, recombine the results of recursively processing its constituent parts, building up a …