Kotlin Ranges
last modified January 29, 2024
This article shows how to work with ranges in Kotlin.
A range is a succession of values between defined lower and upper limits.
A Kotlin range is created with the .. operator or with
the rangeTo and downTo functions.
Kotlin ranges are inclusive by default; that is, 1..3 creates a range
of 1, 2, 3 values. The distance between two values is defined by the
step; the default step is 1.
Kotlin range creation
The following example shows how to create simple ranges in Kotlin.
package com.zetcode
fun main() {
for (i in 1..30)
print("$i ")
println()
for (i in 30 downTo 1)
print("$i ")
println()
for (i in 1.rangeTo(30))
print("$i ")
println()
for (i in 30.downTo(1))
print("$i ")
println()
}
The example creates four ranges of values.
for (i in 1..30)
print("$i ")
The 1..30 creates a succession of values from 1 to 30,
including the bounds. We use the for loop to go through
the range.
for (i in 30 downTo 1)
print("$i ")
With the downTo keyword, we create a succession of values
descending from 30 to 1.
for (i in 1.rangeTo(30))
print("$i ")
The rangeTo function creates a range of values between
the defined bounds; it is an equivalent of the .. operator.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
Kotlin range of characters
We can create a range of characters in Kotlin.
package com.zetcode
fun main() {
for (c in 'a'..'k')
print("$c ")
println()
for (c in 'k' downTo 'a')
print("$c ")
}
The example creates two ranges of letters in ascending and descending orders.
for (c in 'a'..'k')
print("$c ")
We create and print 'a' to 'k' characters.
for (c in 'k' downTo 'a')
print("$c ")
We create and print 'k' to 'a' characters.
a b c d e f g h i j k k j i h g f e d c b a
Kotlin range forEach
We can use the forEach function to traverse the range
of values.
package com.zetcode
fun main() {
(1..5).forEach(::println)
(1..5).reversed().forEach { e -> print("$e ") }
}
The example uses the forEach function to traverse
the ranges.
(1..5).forEach(::println)
With the forEach function, we print all the values from
range 1..5.
(1..5).reversed().forEach { e -> print("$e ") }
In this line, we reverse the range with reversed and
loop over the range with forEach.
1 2 3 4 5 5 4 3 2 1
Kotlin range iterator
We can use the classic iterator to loop over a range in Kotlin.
package com.zetcode
fun main() {
val chars = ('a'..'f')
val it = chars.iterator()
while (it.hasNext()) {
val e = it.next()
println(e)
}
}
The example uses an iterator to loop over a range of characters.
val chars = ('a'..'f')
val it = chars.iterator()
We create a range of characters and an iterator from this range.
while (it.hasNext()) {
val e = it.next()
println(e)
}
In a while loop, we go over the elements of the range. The
hasNext method checks if there is a next
element in the range and the next method returns the
next element in the range.
a b c d e f
Kotlin range step
With the step keyword, we can define a step between
the values of a range.
package com.zetcode
fun main() {
for (e in 1..20 step 2) {
print("$e ")
}
println()
for (e in 1..20 step 5) {
print("$e ")
}
println()
println((1..10 step 2).last)
println((1..10 step 3).first)
println((1..10 step 4).step)
println()
}
The example shows how to use step in Kotlin ranges.
for (e in 1..20 step 2) {
print("$e ")
}
The for loop goes through the values of a range. The range has step 2.
println((1..10 step 2).last) println((1..10 step 3).first) println((1..10 step 4).step)
A Kotlin range contains last, first, and
step attributes, which return the last, first values and the step.
1 3 5 7 9 11 13 15 17 19 1 6 11 16 9 1 4
Kotlin range filter, reduce, map
Kotlin ranges contain filter, reduce, and map operations.
package com.zetcode
fun main() {
val rnums = (1..15)
println(rnums)
val r = rnums.filter { e -> e % 2 == 0 }
println(r)
val r2 = rnums.reduce { total, next -> next * 2 - 1 }
println(r2)
var r3 = rnums.map { e -> e * 5 }
println(r3)
}
The example applies filtering, reduction, and mapping on a range.
val r = rnums.filter { e -> e % 2 == 0 }
With the filter function we filter out even numbers. Even numbers
can be divided by two without a remainder. The operation returns a list of
values.
val r2 = rnums.reduce { total, next -> next * 2 - 1 }
The reduction operation applies the given expression on each of the range elements to produce a single value.
var r3 = rnums.map { e -> e * 5 }
The mapping operation applies the given operation on each of the elements. The mapping returns a list of modified values.
1..15 [2, 4, 6, 8, 10, 12, 14] 29 [5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75]
Kotlin range min, max, sum, average
Kotlin ranges contain predefined reduction operations, including
min, max, sum, and average
package com.zetcode
fun main() {
val r = (1..10)
println(r.min())
println(r.max())
println(r.sum())
println(r.average())
}
The example prints the minimum, maximum, summation, and average of a range of
1..10 values.
1 10 55 5.5
Source
Kotlin ranges and progressions
In this article we have covered Kotlin ranges.
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