:: (a -> a -> Bool) -> [a] -> [[a]] package:vector

O(n) Split a vector into a list of slices. The concatenation of this list of slices is equal to the argument vector, and each slice contains only equal elements, as determined by the equality predicate function.

>>> import qualified Data.Vector.Strict as V

>>> import           Data.Char (isUpper)

>>> V.groupBy (\a b -> isUpper a == isUpper b) (V.fromList "Mississippi River")
["M","ississippi ","R","iver"]

See also groupBy.