Scala foldLeft

In this exercise, you can see two use cases offoldLeft. But first let’s explain the syntax:

foldLeft(initialValue) { case (accumulator, currentElement) => 
    // return the new value of the accumulator
}

Note that whencurrentElementis the first element of theList, thenaccumulatoris equal toinitialValue. Also, if the the list is empty, then the returned value will be theinitialValue.

The returned value can be anything, for instance:

foldLeft(List.empty) { case (accumulator, currentElement) => 
    accumulator :+ currentElement 
}

would return a newListwith the same content as the input list.

An other example:

foldLeft(0) { case (accumulator, currentElement) => 
    accumulator + currentElement 
}

would return the total sum of the item of theList. This is similar to the first example in today’s exercise. And scala provide a shortcut for it:.sum, this would be a special case of the exercise when the initial value is0.

In the second use case, there is a bit more going on. It usespattern matchingto implement different behavior based on the current element and create a new list element by element.

As an extra exercise, try to compute the average of the list by changing the initialized value fromstartFoldto(0, 0)and modify the function to aggregate the values.

You can also try to implementmap,flatMapand,filterusingfoldLeft. Share your solution with our community on Discord !