Notice that in the Scala script shown below, we will be using two different functions, i.e., map and flatten, to achieve the desired functionality. In this example, our goal is to implement a program that can create a map from a list by using the map method of Scala, and then we want to flatten the output of that map by using the flatten method of Scala. Example # 1: Creating a Map from a List in Scala and Flattening its Output without using the FlatMap Method: Now, let us get started by explaining all three of these examples. This will be followed by yet another example in which we will be using the FlatMap method of Scala with a user-defined function. By comparing the two programs and their outputs with each other, you will be able to see how beneficial it is to use the FlatMap method in Scala. After that, we will share another example program that uses the FlatMap method. How to use the FlatMap Method in Scala?įor understanding how the Scala FlatMap method works, we will first show you a program that produces the same results as the FlatMap method would produce. In this guide, we will be talking about the FlatMap method of the Scala programming language that will help us convert a given data structure to a map while flattening its output. Additionally, you might also want to flatten this map, i.e., separate out the elements of this map in the form of distinct characters. You might want to convert a different data structure to a map at times. Therefore, today, we will try to move one step further by introducing you to a very useful function of the Scala programming language, i.e., FlatMap. Therefore, the function you pass to flatMap will always expect to produce a list, and no flatMap function would be expected to know how to act on single elements.We have already talked about the usage of maps in Scala. Note that flatMap has a standard meaning in functional programming, which is, roughly speaking, any mapping function that consumes a single element and produces n elements, but your final result is the concatenation of all of those lists. Types are very often inferred in Scala, and so you're well-served to make sure that the type you're giving is the type expected by the method you're calling. That is the in-the-weeds explanation why the typing is wrong, and is worth explaining because any error that says 'cannot resolve reference with such a signature' means that it can't find a function that takes the explicit type you're offering. List, if you follow it's chain of inheritance up, has this as a trait it is built with, and thus a function that maps from some type A to a List (or any object with the GenTraversableOnce trait) will be a valid function. This is a little difficult to unpack, and I've elided some of it, but the key is the GenTraversableOnce type. So why won't flatMap(f) compile? Let's look at the signature for flatMap, in this case pulled from the List implementation: final override def flatMap(f : scala.Function1])(.) I've rewritten them here, so you can see that f is a function mapping from Int to an (Int, Int) tuple, and g is a function that maps from Int to a List. To understand how this is working, it can be useful to explicitly unpack the functions you're sending to map and flatMap and examine their signatures.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |