groupBy<K> method
Groups elements of the original collection by the key returned by the given keySelector
function
applied to each element and returns a map where each group key is associated with a list of corresponding elements.
The returned map preserves the entry iteration order of the keys produced from the original collection.
Implementation
Map<K, List<T>> groupBy<K>(K Function(T) keySelector) {
return groupByTo({}, keySelector);
}