CODEWITHSUNDEEP
scalafunctional-programming
user5768866
user5768866

Reputation:

When to use fold and when to use foreach in list in Scala

In my understanding, when there is need apply function for each element in list, we use fold function, right?

If just iterate the list, foreach is enough?

Upvotes: 1

Views: 2387

Answers (3)

jacks
jacks

Reputation: 4753

fold

Use fold when you wish to aggregate a set into a single value. Here we say, start at zero and add each successive element to the previous one, then return the result once the set is exhausted.

scala> List(1, 2, 3).foldLeft(0){ (a, b) => a + b }
res10: Int = 6

Note that fold is designed for parallel computation but foldLeft and foldRight are more powerful in terms of what types they can be applied to.

map

Use map when you want to apply a function to each element in the set and return another set with the results.

scala> List(1, 2, 3).map(x => x + x)
res12: List[Int] = List(2, 4, 6)

foreach

Use foreach when you don't want to return anything but need some side effect eg. saving each value to a DB.

List(1, 2, 3).foreach(x => saveToDB(x))

Upvotes: 6

Chirlo
Chirlo

Reputation: 6122

In my understanding, when there is need apply function for each element in list, we use fold function, right?

Nope. You use fold when you want to get a result that is a function of all the elements in the list. That is, you fold the list into one result

To apply the same function on each element of a list, mostly for side effects like printing to screen, you use the foreach, hence the name.

Upvotes: 5

PawelN
PawelN

Reputation: 848

If you want to reduce list you are using fold

List(1,2,3,4).fold(0){_+_} <<-- gives you sum of elements in list

Foreach is used to iterate list and for example print all elements

List(1,2,3,4).foreach(println)

Upvotes: 2

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