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Collections in Kotlin

Fold vs Reduce

fold takes an initial value, and the first invocation of the lambda you pass to it will receive that initial value and the first element of the collection as parameters. reduce doesn't take an initial value, but instead starts with the first element of the collection as the accumulator (called sum in the following example).

Equivalence of the Scala Collection Scan Method

There is no equivalence of the Scala collection scan method. You have to implement it yourself using zip.

until

In [5]:
0.until(3).forEach { println(it) }

0
1
2
Out[5]:
null
In [7]:
(0 until 3).forEach{println(it)}

0
1
2
Out[7]:
null
In [19]:
0.until(9).step(2).forEach { println(it) }

0
2
4
6
8
Out[19]:
null
In [20]:
(0 until 9 step 2).forEach { println(it) }

0
2
4
6
8
Out[20]:
null

rangeTo

rangeTo is inclusive on both ends.

In [3]:
0.rangeTo(3).forEach{
    println(it)
}

0
1
2
3
Out[3]:
null
In [9]:
(0..3).forEach{
    println(it)
}

0
1
2
3
Out[9]:
null
In [17]:
0.rangeTo(9).step(2).forEach { println(it) }

0
2
4
6
8
Out[17]:
null
In [16]:
(0..9 step 2).forEach { println(it) }

0
2
4
6
8
Out[16]:
null

downTo

downTo is inclusive on both ends.

In [4]:
3.downTo(0).forEach{ println(it) }

3
2
1
0
Out[4]:
null

References

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.ranges/until.html

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.ranges/range-to.html

https://stackoverflow.com/questions/44429419/what-is-basic-difference-between-fold-and-reduce-in-kotlin-when-to-use-which

https://kotlinlang.org/docs/reference/ranges.html

In [ ]:

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