We can now use listMonad’s flatten method to flatten a List of Lists :Īssert(listMonad. Override def flatMap(ma: List)(f: A ⇒ List): List = ma flatMap f So flatMapping a function is just mapping the function first and then flattening the result.įlattening is just flatMapping identity – flatMapping is mapping and then flattening Thus the getOrElse in flatMap to get the will either. Int > Option String Then for map, B Option String and will return Option Option String. flatMap is a combination of map and flatten, so it first runs map on the sequence, then runs flatten, giving the result shown. In the second monad trait, flatMap is defined in terms of map and flatten: When you call flatMap and pass the function A > Option B, flatMap calls map and passes the same function, but the B in flatMap is not same B as in map. Because flatMap treats a String as a sequence of Char, it flattens the resulting list of strings into a sequence of characters ( Seq Char ). So flattening is just flatMapping the identity function x => x. In the first monad trait, flatten is defined in terms of flatMap:ĭef flatten(mma: F]): F = flatMap(mma)(ma => ma) Returning the resultingğ], it flattens it and returns anğ. What it does is apply to eachĚ element of ma a function f producing anğ, but instead of
The flatMap function takes anğ and a function fromĚ toğ and returns anğ The flatten function takes anğ] and returns anğ Here is a monad trait implementing monadic combinators unit and flatMapĭef flatMap(ma: F)(f: A ⇒ F): Fĭef map(m: F)(f: A ⇒ B): F = flatMap(m)(a ⇒ unit(f(a)))ĭef flatten(mma: F]): F = flatMap(mma)(ma ⇒ ma)Īnd here is a monad trait implementing monadic combinators unit, map and flattenĭef flatMap(ma: F)(f: A ⇒ F): F = flatten(map(ma)(f)) Scala collection methods flatMap and flatten are more powerful than monadic flatMap and flattenĪ monad is an implementation of one of the minimal sets of monadic combinators, satisfying the laws of associativity and identity. Val combinations = numbers.flatMap(n => chars.flatMap(c => colors.Scala collection methods flatMap and flatten are more powerful than monadic flatMap and flatten (download for better quality) Println(list.filter(_ % 2 = 0)) // prints 2įlatten (reduces) the hierarchy by one level each time it is applied Map operation is one step behind flatMap operation technique and is mostly similar. This gives many results out of it which means that we can get one, two, zero and other many elements from the flatMap operation applications. A new RDD is returned with its application on each element of RDD as a result.
FLATMAP SCALA HOW TO
How to convert this map/flatMap into a for comprehension, and please explain how. A flatMap is an operation of transformation. Values are filtered when boolean is true. Tags: scala, monads, for-comprehension Answers: 1 Viewed 10,032 times. Create a new Scala sbt project in IntelliJ IDEA with a name ActionMovies and add the following dependencies to the build.sbt file. Takes a lambda that takes one param and returns boolean. Println(list.map(_ + " is a number")) // returns List (same type) of type String Println(list.map(_ + 1)) // returns List (same type) of type Int
Val list = List(1,2,3) // this is calling apply method on companion object For instance: scala> List(1, 2, 3) map ( + 1) res29: ListInt List(2.
When map is applied on some collection of type A, it returns a new collection of the same type with elements of type B. Mapping over lists: map, flatMap and foreach The operation xs map f takes as.
Novemby Niranjan Tallapalli Leave a comment
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