CODEWITHSUNDEEP
javamatrix
NeptaliD
NeptaliD

Reputation: 35

Matrix Manipulation Java

let's assume that I have the next two dimensional int array:

  int [][] mat = {{1 1 1 1 1}, 
                  {0 0 0 0 0}, 
                  {3 3 3 3 3}, 
                  {0 0 0 0 0}, 
                  {2 2 2 2 2}};

the reason i'm here is because I'm trying to think of a way to shuffle the rows in the next order (without losing the first row data): 

   first row data -> second row 
   second row data -> third row
   third row data -> fourth row
   fourth row data -> fifth row

a more detailed graphic explanation of what i've written:

    original: 1 1 1 1 1      what i need: 1 1 1 1 1 
              0 0 0 0 0                   1 1 1 1 1 <- first row data on the second row
              3 3 3 3 3                   0 0 0 0 0 <- second row data on the third row
              0 0 0 0 0                   3 3 3 3 3 <- third row data on the fourth row
              2 2 2 2 2                   0 0 0 0 0 <- fourth row data on the fifth row

     meaning that the 1st row always remains constant 
     and that the original fifth row always loses its content

Any suggestion/tips of how I would implement such thing would be highly appreciated!

Upvotes: 1

Views: 189

Answers (4)

BradzTech
BradzTech

Reputation: 2835

If you want to preserve row 0, you should loop from row 1 to the last row, setting the value of the previous row to the value of the current row.

Here's a simple, intuitive example which copies the values of every column of the array:

for (int i = 1; i < mat.length; i++) {
    for (int j = 0; j < mat[i].length; j++) {
        mat[i][j] = mat[i - 1][j]
    }
}

Upvotes: 0

pilu
pilu

Reputation: 800

All you have to do here, is replace every row by its previous one. This can be easily achieved by looping through the columns with a reverse order, i.e your outer for loop will iterate backwards. Make sure to stop at the 2nd row (its index is 1 so that you maintain the original 1st row):

for (int i = mat.length-1; i>0; i--) {
  // copy mat[i-1] into mat[i] for every element of this row
}

Upvotes: 1

Mohamed Gad-Elrab
Mohamed Gad-Elrab

Reputation: 646

you can easily use Arrays.CopyOf() and for each row copy the previous one

So, the code should be something like

public static void main (String[] args) throws java.lang.Exception
{
    int [][] mat = new int[][]{{1,1,1,1,1}, 
              {0, 0, 0 ,0 ,0}, 
              {3, 3, 3, 3, 3}, 
              {0, 0 ,0, 0, 0}, 
              {2 ,2, 2 ,2 ,2}};


for(int i=mat.length-1;i>0;i--){

     mat[i]=Arrays.copyOf(mat[i-1],mat[i-1].length);
}

// To check correctness
for(int i=0;i<mat.length;i++){

     System.out.println(Arrays.toString(mat[i]));
}


}

Upvotes: 0

Frank Puffer
Frank Puffer

Reputation: 8215

Iterate backwards from the last row to the second one.

For each of these rows, assign the values from the previous row to it.

Upvotes: 1

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