Initialize Array of LongArray in Kotlin

Question

I basically wanted to create 2D array whose size is known to me on runtime

I have declare and array of LongArray as below

private lateinit var optionalGroup: Array<LongArray>

And I can assign value to it as below where group is my Mutable Map

 group.forEach { (key, value) -> optionalGroup[key - 1] = LongArray(value) }

My question is how can I initialize optionalGroup with size as of group ? I tried

`optionalGroup = Array(group.size)

thows error No value passed for parameter 'init'`

To create an array you need to pass the initial values of the array. Array(group.size) { LongArray(0) } should work, but you will also overwrite all the values later. Consider using a MutableList instead. — m0skit0
– m0skit0, Commented Feb 12, 2019 at 11:44

m0skit0 · Accepted Answer · 2019-02-12 11:54:59Z

2

If you use an array, you have no choice but to initialize the initial values of each element

optionalGroup = Array(group.size) { LongArray(0) }

I suggest you use a mutable list instead to avoid having to initialize the elements:

private lateinit var optionalGroup: MutableList<LongArray>
optionalGroup = mutableListOf()

If this is not an option, you can still use a temporary mutable list and convert it back to a typed array:

val tempList = mutableListOf<LongArray>()
group.forEach { (key, value) -> tempList[key - 1] = LongArray(value) }
optionalGroup = tempList.toTypedArray()

edited Feb 12, 2019 at 11:54

answered Feb 12, 2019 at 11:41

m0skit0

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1 Comment

m0skit0 Over a year ago

Generally you should avoid arrays and use lists whenever possible ;)

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