88th: Scala uses the for expression to implement map, FLATMAP, filter

Today we will learn how to use the for expression to implement map, Flatmap, and filter

First, let's look at the map. The function of map is to pass in a list, through a function f, to change the element A in list to the process of element B. Finally get the list formed by B. If this process is implemented by a For loop, the following actions are performed:

for (element <-list) yield f (Element)

Next we look at the Flatmap. The function of Flatmap is to pass in a list, through a function f, to convert each element of the list into a list, and finally to return a list of all the elements in those lists. This process, if implemented by the for expression, operates as follows: for (X<-list;y<-f (x)) yield y

Finally, we look at the filter operation, the function of filter is to pass in a list of lists, through the function F, filter out the Boolean expression is true, that is, the eligible elements, and finally return the list of elements that meet the criteria. This process, if implemented by the for expression, operates as follows: for (Elem <-list if f (elem)) yield Elem

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88th: Scala uses the for expression to implement map, FLATMAP, filter