The foreach Loop in Scala

1. Using foreach Loop in Scala
2. Using foreach Loop With until Flag in Scala
3. Using foreach Loop With if Condition in Scala
4. Using foreach Loop With yield in Scala
5. Using foreach Loop to Iterate List in Scala
6. Using the foreach() Function of Scala
7. Using the foreach Function With Vector in Scala

foreach is a loop used to iterate over the elements of an object/container. This tutorial will discuss the foreach loop and learn how to implement it in Scala.

Using foreach Loop in Scala

Scala provides a foreach() function to traverse list elements. We created a foreach loop that traverses numerical values to the specified limit in this example.

The loop requires two arguments, the first is the loop’s starting, and the second is the end.

Example:

object MyClass {
    def main(args: Array[String]) {
        print("for loop iterating...\n")
        for( a <- 1 to 3 ){
         println(a);
        }
    }
}

Output:

for loop iterating...
1
2
3

Using foreach Loop With until Flag in Scala

We will create a foreach loop with the until flag to traverse numerical values. It is useful when iterating the elements but excluding the last ones.

The loop requires two arguments, the first is the loop’s starting, and the second is the until keyword.

Example:

object MyClass {
    def main(args: Array[String]) {
        print("for loop iterating...\n")
        for( a <- 1 until 3 ){
         println(a);
        }
    }
}

Output:

for loop iterating...
1
2

Using foreach Loop With if Condition in Scala

If you want to filter the data while traversing, you can use the if condition with the loop expression. This is Scala’s way to get filtered data with concise code.

Here in the code snippet below, we only used the if condition in the loop to get even values.

Example:

object MyClass {
    def main(args: Array[String]) {
        print("for loop iterating...\n")
        for( a <- 1 to 10 if a%2==0 ){
            println(a);
        }
    }
}

Output:

for loop iterating...
2
4
6
8
10

Using foreach Loop With yield in Scala

If you want to get a collection of items after traversing rather than traversing and displaying elements, then use the yield keyword with the loop.

The yield keyword returns a collection of the same traversed type, which means map returns map and list returns a list. Here, we traversed numeric values and got a vector after iterations of the loop.

Example:

object MyClass {
    def main(args: Array[String]) {
        print("for loop iterating...\n")
        var result = for( a <- 1 to 5) yield a
        print(result)
    }
}

Output:

for loop iterating...
Vector(1, 2, 3, 4, 5)

Using foreach Loop to Iterate List in Scala

Apart from imperative use, we can use the foreach loop to iterate list elements. While working with built-in collections, we don’t need to specify any endpoint of the loop or until keyword as the Scala interpreter handles it and exit the loop when no elements are left in the collection.

Example:

object MyClass {
    def main(args: Array[String]) {
        print("for loop iterating...\n")
        var list = List(1,52,35,6,8,9)
        for( i <- list){
            println(i)
        }
    }
}

Output:

for loop iterating...
1
52
35
6
8
9

Using the foreach() Function of Scala

Scala provides a built-in foreach() function in the List class to iterate the list elements, so we no longer need to use a loop. As an argument, this function accepts a lambda expression and returns the result.

Here, we passed the print statement to the foreach() to print the elements to the console.

Example:

object MyClass {
    def main(args: Array[String]) {
        print("for loop iterating...\n")
        var list = List(1,52,35,6,8,9)
        list.foreach(println)
    }
}

Output:

for loop iterating...
1
52
35
6
8
9

Below is another example where we get the sum of all the elements of the list by just passing an expression. We passed the expression to get a sum rather than a print statement.

object MyClass {
    def main(args: Array[String]) {
        var sum = 0;
        print("for loop iterating...\n");
        var list = List(1,5,35,6,8,9);
        list.foreach(sum += _)
        print(sum);
    }
}

Output:

for loop iterating...
64

Using the foreach Function With Vector in Scala

We can use the foreach function with Vector similarly to traverse the elements. Vector is a sequence in Scala that holds the elements in key and value pairs.

Example:

object MyClass {
    def main(args: Array[String]) {
        print("foreach loop iterating...\n");
        val nums = Vector((1,8), (2,9), (3,7), (4,6), (5,5))
        nums.foreach {
            case(key, value) => println(s"key: $key, value: $value")
        }
    }
}

Output:

foreach loop iterating...
key: 1, value: 8
key: 2, value: 9
key: 3, value: 7
key: 4, value: 6
key: 5, value: 5