Kotlin - Ranges


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Kotlin range is defined by its two endpoint values which are both included in the range. Kotlin ranges are created with rangeTo() function, or simply using downTo or (. .) operators. The main operation on ranges is contains, which is usually used in the form of in and !in operators.

Example

1..10  // Range of integers starting from 1 to 10

a..z   // Range of characters starting from a to z

A..Z   // Range of capital characters starting from A to Z

Both the ends of the range are always included in the range which means that the 1..4 expression corresponds to the values 1,2,3 and 4.

Creating Ranges using rangeTo()

To create a Kotlin range we call rangeTo() function on the range start value and provide the end value as an argument.

Example

fun main(args: Array<String>) {
   for ( num in 1.rangeTo(4) ) {
     println(num)
   }
}

When you run the above Kotlin program, it will generate the following output:

1
2
3
4

Creating Ranges using .. Operator

The rangeTo() is often called in its operator form ... So the above code can be re-written using .. operator as follows:

Example

fun main(args: Array<String>) {
   for ( num in 1..4 ) {
     println(num)
   }
}

When you run the above Kotlin program, it will generate the following output:

1
2
3
4

Creating Ranges using downTo() Operator

If we want to define a backward range we can use the downTo operator:

Example

fun main(args: Array<String>) {
   for ( num in 4 downTo 1 ) {
     println(num)
   }
}

When you run the above Kotlin program, it will generate the following output:

4
3
2
1

Kotlin step() Function

We can use step() function to define the distance between the values of the range. Let's have a look at the following example:

Example

fun main(args: Array<String>) {
   for ( num in 1..10 step 2 ) {
     println(num)
   }
}

When you run the above Kotlin program, it will generate the following output:

1
3
5
7
9

Kotlin range of Characters

Ranges can be created for characters like we have created them for integer values.

Example

fun main(args: Array<String>) {
   for ( ch in 'a'..'d' ) {
     println(ch)
   }
}

When you run the above Kotlin program, it will generate the following output:

a
b
c
d

Kotlin reversed() Function

The function reversed() can be used to reverse the values of a range.

Example

fun main(args: Array<String>) {
   for ( num in (1..5).reversed() ) {
     println(num)
   }
}

When you run the above Kotlin program, it will generate the following output:

5
4
3
2
1

Kotlin until() Function

The function until() can be used to create a range but it will skip the last element given.

Example

fun main(args: Array<String>) {
   for ( num in 1 until 5 ) {
     println(num)
   }
}

When you run the above Kotlin program, it will generate the following output:

1
2
3
4

The last, first, step Elements

We can use first, last and step properties of a range to find the first, the last value or the step of a range.

Example

fun main(args: Array<String>) {
   println((5..10).first)
   println((5..10 step 2).step)
   println((5..10).reversed().last)
}

When you run the above Kotlin program, it will generate the following output:

5
2
5

Filtering Ranges

The filter() function will return a list of elements matching a given predicate:

Example

fun main(args: Array<String>) {
   val a = 1..10
   val f = a.filter { T -> T % 2 == 0 }
   
   println(f)
}

When you run the above Kotlin program, it will generate the following output:

[2, 4, 6, 8, 10]

Distinct Values in a Range

The distinct() function will return a list of distinct values from a range having repeated values:

Example

fun main(args: Array<String>) {
   val a = listOf(1, 1, 2, 4, 4, 6, 10)
   
   println(a.distinct())
}

When you run the above Kotlin program, it will generate the following output:

[1, 2, 4, 6, 10]

Range Utility Functions

There are many other useful functions we can apply to our range, like min, max, sum, average, count:

Example

fun main(args: Array<String>) {
   val a = 1..10
   
   println(a.min())
   println(a.max())
   println(a.sum())
   println(a.average())
   println(a.count())
}

When you run the above Kotlin program, it will generate the following output:

1
10
55
5.5
10

Quiz Time (Interview & Exams Preparation)

Q 2 - What will be the output of the following program:

fun main(args: Array<String>) {
   val a = 1..20
   
   println(a.average())
}

A - This will print 10.5

B - This will raise just a warning

C - Compilation will stop with error

D - None of the above

Answer : A

Explanation

Function average() is used to get the average of the range values.

Q 2 - What will be the output of the following program:

fun main(args: Array<String>) {
   val a = 1..20
   
   if( 3 in a){
      print( true )
   }else{
      print( false )
   }
}

A - true

B - false

C - Compilation will stop with error

D - None of the above

Answer : A

Explanation

It will return true because 3 is available in range so in operator will return true.

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