Convert Array<Int> to Int kotlin 2D Array

Question

Is there a way to convert an Array<Int> to an Int in Kotlin? I am messing with 2D arrays and am trying to print the elements whose indexes are equal to each other. Here is my loop that tries to accomplish this:

     for (rows in arr) {
         for (elements in rows) {
-------->    if (rows == elements) {
                 print(elements)
             }
         }
         print("\n")
     }

rows is type Array<Int> and elements is type Int. I have already tried using the StringBuilder method and that does not work. Is there a function or other method that allows this? Any tips for me to do further research is appreciated.

Could your give an example of what the output should look like? — Alexander Egger
– Alexander Egger, Commented Mar 19, 2019 at 5:45
Of course. Lets say arr = [1,2] [3,4]. The output should be 1,4 since 1 is at index[0][0] and 4 is at index[3][4] — ntrix
– ntrix, Commented Mar 19, 2019 at 5:48
So is this question about finding the diagonal of a square array? — gidds
– gidds, Commented Mar 19, 2019 at 7:47
I did mean 4 is at [1][1]. The question is not about finding the diagonal of a square array. I understand that if(i < j) then all of the elements below the main diagonal would be printed out. The solution that @andras stated showed me that there is a .size function to get the entire length of the array and that was my missing piece to my problem. — ntrix
– ntrix, Commented Mar 19, 2019 at 17:07

andras · Accepted Answer · 2019-03-19 06:33:52Z

Here is one way with foreach. The key is that you either iterate by indices, or you iterate by mapping the existing value with an index.

3 ways to solve this:

Any programming language styled:

    for(rowIndex in 0 until arr.size) {
        for(colIndex in 0 until arr[rowIndex].size) {
            if(colIndex == rowIndex) {
                println("[$rowIndex, $colIndex]: ${arr[rowIndex][colIndex]}")
            }
        }
    }

Python styled: (and using destructuring syntax)

    for ((rowIndex, row) in arr.withIndex()) {
        for ((colIndex, value) in row.withIndex()) {
            if(colIndex == rowIndex) {
                println("[$rowIndex, $colIndex]: $value")
            }
        }
    }

Same as previous, but using lambdas:

   arr.withIndex().forEach {
        (rowIndex, row) ->
        row.withIndex().forEach { (colIndex, value) ->
            if(colIndex == rowIndex) {
                println("[$rowIndex, $colIndex]: $value")
            }
        }
    }

s1m0nw1 · Accepted Answer · 2019-03-19 07:20:01Z

0

I'd probably do something like this:

arr.indices.forEach { i ->
    arr[i].indices.forEach { j ->
        if (i == j) println("arr[$i][$j]==${arr[i][j]}")
    }
}

The indices extension is just one way but since you're mostly interested in them I think it's a good solution.

answered Mar 19, 2019 at 7:20

s1m0nw1

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1 Comment

Alexey Romanov Over a year ago

I would prefer for because of stackoverflow.com/questions/52904923/… (it doesn't seem to have changed since then).

Alexey Romanov · Accepted Answer · 2019-03-19 09:46:37Z

0

If there is only one element in an array you want, and you know its index, there is absolutely no reason to iterate over the array. So I would suggest

for (i in arr.indices) {
    if (i < arr[i].size) {
        println("arr[$i][$i]==${arr[i][i]}")
    }
}

answered Mar 19, 2019 at 9:46

Alexey Romanov

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Comments

Pravin Londhe · Accepted Answer · 2019-03-19 09:58:01Z

0

You can see following function

fun printDiagonalElements(){
    val row1 = intArrayOf(1,2,3)
    val row2 = intArrayOf(4,5,6)
    val row3 = intArrayOf(7,8,9)
    val row4 = intArrayOf(10,5,6,16)
    val array : Array<IntArray> = arrayOf(row1,row2,row3,row4)

    for(i in 0 .. array.size-1){
        val row = array[i]
        for (j in 0 .. row.size-1){
            if(i == j){
                println(array[i][j])
            }
        }
    }
}

answered Mar 19, 2019 at 9:58

Pravin Londhe

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Comments

Ilya · Accepted Answer · 2019-03-19 18:00:07Z

0

I'm not sure why every proposed solution here iterates the elements inner array if only one its value is required.

Here is a way to print numbers in the main diagonal of a square 2D array with one loop:

arr.forEachIndexed { index, row -> 
    println("value at [$index, $index]: ${row[index]}")
}

Note however that this will throw if there are more rows than columns in this array, i.e. if the array is not square. You can add a check to ensure that there's a column with the row index in each row array:

arr.forEachIndexed { index, row -> 
    if (index in row.indices) {
        println("value at [$index, $index]: ${row[index]}")
    }
}

answered Mar 19, 2019 at 18:00

Ilya

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