Main Points About Kotlin Range

Syntax of creating a range

The general way of creating a range in Kotlin is:

for example:

for (i in 1..10){

//statement to execute here

}

This is equivalent of:

An example of creating a range

In this example, a simple range is created and used inside the for loop.

The range starting value is 0 and the end value is 5.

See how we iterate through the range and display its items and also notice the step value, start and end inclusive values:

fun main(args: Array<String>) {

 //creating the range

    for (x in 0..5)

        println("$x ")

    }

The output:

The example of using rangeTo function

As mentioned earlier, you may also use rangeTo() and downTo() functions rather than .. (double dots).

The example below creates a range and is again used in the for loop to display its items.

See how it is created with rangeTo() function:

fun main(args: Array<String>) {

 //creating the range with rangeTo()

    for (i in 6.rangeTo(10))

        println("$i ")

    }

The output:

The range example with downTo() function

The example below uses downTo() function in the range.

In above two examples, the range goes upwards i.e. from 1….to 5 or 10. If you want to go downwards then you may use the downTo(). See the example below:

fun main(args: Array<String>) {

 //creating the range with downTo()

    for (x in 15 downTo 11)

        println("$x ")

    }

The result:

You can see, the count goes downwards from 15 to 11.

An example of creating a character range

Above, we see the ranges of numbers in two different ways. In this example, a range of characters is created from ‘a’ to ‘i’ with the step of one by using the .. operator:

fun main(args: Array<String>) {

 //creating the character range

    for (charter in 'a'..'i')

        print("$charter ")

}

The result:

Using downTo() function for char range

See how we step down in the case of creating a char range:

fun main(args: Array<String>) {

 //creating the character range with downTo()

    for (x in 'i' downTo 'a')

        print("$x ")

 }

The output:

You saw, the range started from character ‘i’ and ended at ‘a’.

The example of step in number range

Now let us look at using the step() function as creating a range.

As said earlier, the default step is 1; as we have also seen in all the above examples, whether going upwards or downwards.

By using the step() function, we will create a range with a gap of 5; see how:

fun main(args: Array<String>) {

    //creating the range with step

    for (x in 5..25 step 5)

        println("$x ")

 }

The output:

Using step with downTo function

The example below shows using the step() function with downTo(). I created a range from 100 to 1 with a gap of 20:

fun main(args: Array<String>) {

    //downTo() and step()

    for (x in 100 downTo 1 step 20)

        println("$x ")

 }

The output:

Using step() in char range example

Similarly, the step can be specified in the char range as follows:

fun main(args: Array<String>) {

    //char range with step()

    for (chr in 'a'..'i' step 2)

        print("$chr ")

}

Output:

Using step and downTo() with char range

Similarly, you may use the step function with the downTo() in the case of char range:

fun main(args: Array<String>) {

    for (chr in 'h' downTo 'b' step 2)

        print("$chr ")

}

The result:

Excluding the end value by until() function

Until now, we have seen the ranges created with start and end values inclusive. Sometimes, you may be required to exclude the given end value in the range.

For that, you may use the until() function as shown in the code below:

fun main(args: Array<String>) {

    for (num in 1 until 5)

        println(num)

}

The output:

It can be seen that 5 is not displayed which is the end range value.

Range utility functions examples

In Kotlin, the range has a few simple utility functions that can be used for range simple tasks.

For example, getting the minimum and maximum value in the range. Similarly, the average value of the range, the sum of range, the total count of the items in the range, etc.

For that, Kotlin range has the following functions:

• count()
• average()
• min()
• max()
• sum()

The example below creates a number range and then I used these functions to get the results:

fun main(args: Array<String>) {

//get minimum, maximum, count, sum and average

    val a_range = 1..10

    println("Total Items = "  +a_range.count())

    println("Sum of range = "  +a_range.sum())

    println("Range Average = "  +a_range.average())

    println("Minimum value in range = "  +a_range.min())

    println("Maximum value in range = " +a_range.max())

}

The result:

Using the iterator function example

Finally, you may also iterate through a range by using iterator() function. For that, you may use the hasNext() and next() methods as follows:

fun main(args: Array<String>) {

//iterator function example

    val nums = (5..25 step 5)

    val i = nums.iterator()

    while (i.hasNext()) {

        val j = i.next()

        println(j)

    }

}

The output of the above code: