Append List of array to an array and repeat this in kotlin-CodePudding

I can't seem to find a right solution. Trying to add a list of array to another array. With my Python background it is easily done but not in Kotlin.

fun main() {
   val even = arrayOf(2, 4, 6)
   val odd = arrayOf(1, 3, 5)

   val arr1 = arrayOf(even, odd)
   val extra = arrayOf(7,7,7)
   val arr2 = arrayOf(arr1, extra)

   print(arr2.contentDeepToString())
}

When executing above code I receive...

[[[2, 4, 6], [1, 3, 5]], [7, 7, 7]]

What I want to achieve is this ....

[2, 4, 6], [1, 3, 5], [7, 7, 7]

CodePudding user response：

To add a thing to an array of things, and produce a new array, use plusElement:

val arr2 = arr1.plusElement(extra)

This not only works for arrays, but also works for any Iterables, i.e. Lists, Sets etc.

CodePudding user response：

Do you get why you're getting that result? arrayOf(items) creates a new array wrapping those items, so arrayOf(even, odd) is an array that contains two arrays. Then you create another array, containing that array-of-arrays and another single array. You're nesting them as you go

Sweeper's answer is probably what you want, but there are a lot of ways to combine collections, flatten sequences etc. Like one thing you can do is use the *operator (the "spread operator") to "unpack" your arrays, so you get the items instead:

   // unpack arr1 from an array of arrays, into just those arrays
   // equivalent to arrayOf([2, 4, 6], [1, 3, 5], extra)
   val arr2 = arrayOf(*arr1, extra)

   print(arr2.contentDeepToString())
   >> [[2, 4, 6], [1, 3, 5], [7, 7, 7]]

There's also flatMap, flatten etc - the best option depends on what you're doing!

Also when you say you want this:

[2, 4, 6], [1, 3, 5], [7, 7, 7]

that's just a bunch of values, not contained in anything, so we're assuming you want this:

[[2, 4, 6], [1, 3, 5], [7, 7, 7]]

where they're held in an array (or it could be a list). You could use the spread operator to unpack that into a bunch of values, but all you can do with that is pass it as a variable number of arguments to a function (which is what's happening in arrayOf)

CodePudding user response：

I assume you want to get the following array:

[[2, 4, 6], [1, 3, 5], [7, 7, 7]]

There is an overridden (plus) operator for Arrays in Kotlin, you can use it for adding arrays:

val arr2 = arr1   extra

Resulting array arr2 will contain all elements of the original array arr1 and then all elements of the array extra.