reduceIndexedOrNull
inline
fun
<
S
,
T
:
S
>
Array
<
out
T
>
.
reduceIndexedOrNull
(
operation
:
(
index
:
Int
,
acc
:
S
,
T
)
->
S
)
:
S
?
(source)
inline
fun
ShortArray
.
reduceIndexedOrNull
(
operation
:
(
index
:
Int
,
acc
:
Short
,
Short
)
->
Short
)
:
Short
?
(source)
inline
fun
FloatArray
.
reduceIndexedOrNull
(
operation
:
(
index
:
Int
,
acc
:
Float
,
Float
)
->
Float
)
:
Float
?
(source)
inline
fun
DoubleArray
.
reduceIndexedOrNull
(
operation
:
(
index
:
Int
,
acc
:
Double
,
Double
)
->
Double
)
:
Double
?
(source)
inline
fun
BooleanArray
.
reduceIndexedOrNull
(
operation
:
(
index
:
Int
,
acc
:
Boolean
,
Boolean
)
->
Boolean
)
:
Boolean
?
(source)
Accumulates value starting with the first element and applying operation from left to right to current accumulator value and each element with its index in the original array.
Returns
null
if the array is empty.
import kotlin.test.*
fun main(args: Array<String>) {
//sampleStart
val strings = listOf("a", "b", "c", "d")
println(strings.reduceOrNull { acc, string -> acc + string }) // abcd
println(strings.reduceIndexedOrNull { index, acc, string -> acc + string + index }) // ab1c2d3
println(emptyList<String>().reduceOrNull { _, _ -> "" }) // null
//sampleEnd
}
Parameters
operation
- function that takes the index of an element, current accumulator value and the element itself,
and calculates the next accumulator value.
Accumulates value starting with the first element and applying operation from left to right to current accumulator value and each element with its index in the original collection.
Returns
null
if the collection is empty.
import kotlin.test.*
fun main(args: Array<String>) {
//sampleStart
val strings = listOf("a", "b", "c", "d")
println(strings.reduceOrNull { acc, string -> acc + string }) // abcd
println(strings.reduceIndexedOrNull { index, acc, string -> acc + string + index }) // ab1c2d3
println(emptyList<String>().reduceOrNull { _, _ -> "" }) // null
//sampleEnd
}
Parameters
operation
- function that takes the index of an element, current accumulator value and the element itself,
and calculates the next accumulator value.