CODEWITHSUNDEEP
javaarraysmultidimensional-array
Dheeraj Thakur
Dheeraj Thakur

Reputation: 3

Converting 2D array to 1D Array without using ArrayList

Create Function for Convert 2d array into 1D array

But at Declaration time the size of 1D array how to give size to the new 1D array

int[] convert(int[][] input){
    int[] result;
    int z=0;
    for(int row=0;row<input.length;row++) {
        for(int col=0;col<input[row].length;col++) {
            result[z]=input[row][col];
            z++;
        }
    }
    return result;/* Error comes here For Initialization. How to initialize before Knowing size*/
}

Upvotes: 0

Views: 1582

Answers (5)

GEORGE
GEORGE

Reputation: 1

The below code converts / flattens 2D array to 1D (row-wise)

(MxM)- Row Wise

 private static int[] convert2Dto1DArrayMxM(int[][] input) {

    //Get total elements to calculate the length of result Array
    //Since it is MXM totalElements calculation is = rowsLength x row[0].length

    int totalElements = input.length * input[0].length;

    //Populate the result Array

    int[] result = new int[totalElements];
    int resultIndex = 0;
    for (int row = 0; row < input.length; row++) {
        for (int col = 0; col < input[0].length; col++) {
            result[resultIndex] = input[row][col];
            resultIndex++;
        }
    }
    return result;
}

(MxN)- Row Wise

private static int[] convert2Dto1DArrayMxN(int[][] input) {
    
   //Get total elements in input array to calculate the length of result Array

    int totalElements = 0;
    for (int row = 0; row < input.length; row++) {
        for (int col = 0; col < input[row].length; col++) {
            totalElements++;
        }
    }

    //Populate the result Array

    int[] result = new int[totalElements];
    int resultIndex = 0;

    for (int row = 0; row < input.length; row++) {
        for (int col = 0; col < input[row].length; col++) {
            result[resultIndex] = input[row][col];
            resultIndex++;
        }
    }

    return result;
}

(MxM)- Column Wise

 private static int[] convert2Dto1DArrayMxMColumnWise(int[][] input) {

    //Get total elements to calculate the length of result Array
    //Since it is MXM totalElements calculation is = rowsLength x row[0].length

    int totalElements = input.length * input[0].length;

    //Populate the result Array

    int[] result = new int[totalElements];
    int resultIndex = 0;
    for (int column = 0; column < input[0].length; column++) {
        for (int row = 0; row < input.length; row++) {
            result[resultIndex] = input[row][column];
            resultIndex++;
        }
    }
    return result;
}

How to use:

  public static void main(String[] args) {

     //MXM - Row Wise

    int[][] mXm = {{2, 19}, {6, 80}, {42, 10}};
    int[] mXmResult = convert2Dto1DArrayMxM(mXm);
    System.out.println(Arrays.toString(mXmResult));

    //MXN - Row Wise

    int[][] mXn = {{2, 19, 0, 1, 4, 6, 3, 2, 1, 6}, {2, 0}, {2, 0, 1, 5}};
    int[] mXnResult = convert2Dto1DArrayMxN(mXn);
    System.out.println(Arrays.toString(mXnResult));

    //MxM - Column Wise

    int[][] mXmColumnWise = {{2, 19,10}, {6, 80,9}};
    int[] mXmResultColumnWise = convert2Dto1DArrayMxMColumnWise(mXmColumnWise);
    System.out.println(Arrays.toString(mXmResultColumnWise));
}

Sample output for the above main()

MxM - Row Wise [2, 19, 6, 80, 42, 10]

MxN - Row Wise [2, 19, 0, 1, 4, 6, 3, 2, 1, 6, 2, 0, 2, 0, 1, 5]

MxM - Column Wise [2, 6, 19, 80, 10, 9]

Upvotes: 0

Eritrean
Eritrean

Reputation: 16508

Or you could just use streams with out to have to take care of size by yourself:

int[] convert(int[][] input){    
    return Stream.of(input).flatMapToInt(x -> Arrays.stream(x)).toArray();
}

Upvotes: 0

Kiran H M
Kiran H M

Reputation: 1

1)If it is rectangular 2D array, compute the size this way

int array[]  = new int[input.length * input[0].length];

2)If it is not rectangular, iterate through each row and add the length of each sub-array

int size = 0;
for(int i=0;i<input.length;i++){
 size += input[i].length;
}

Upvotes: 0

Pavneet_Singh
Pavneet_Singh

Reputation: 37414

if rows and columns are balanced 

int result[] = new int[input.length * input[0].length];

otherwise, you have to loop through the whole array while keeping a count of length

int len = 0;
for(int[] a : input){
    len+=a.length;
}
int[] result = new int[len];

Upvotes: 5

Arnaud
Arnaud

Reputation: 17534

You can simply compute the size this way (i.e number of rows * number of columns):

int[] result = new int[input.length * input[0].length] ;

Upvotes: 1

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