inline fun <T, K> MongoIterable<T>.groupingBy(crossinline keySelector: (T) -> K): Grouping<T, K> (source)
Creates a Grouping source from a collection to be used later with one of group-and-fold operations using the specified keySelector function to extract a key from each element.
//Unresolved: samples.collections.Collections.Transformations.groupingByEachCount