I am looking for a way to traverse a 2d n by m int array (int[col][row]) first row by row (simple part) and then column by column, in Java. Here is the code for doing row by row, is there a way to do col by col?
for(int i = 0; i < display.length; i++){
for (int j = 0; j < display[i].length; j++){
if (display[i][j] == 1)
display[i][j] = w++;
else w = 0;
}
}
Since you used a two dimensional array as a matrix, we can assume that the length of each row is the same throughout the matrix (i.e. number of columns of each row is the same).
//So, you can treat display[0].length as the number of columns.
for(int col=0; col<display[0].length; col++)
{
for(int row=0; row<display.length; row++)
{
//your code to access display[row][col]
}
}
Hope this helps!
Here is one approach that will print by column if the row has that many columns column.
String[][] twoDArray = new String[][] {
new String[] {"Row1Col1", "Row1Col2", "Row1Col3"},
new String[] {"Row2Col1", "Row2Col2"},
new String[] {"Row3Col1", "Row3Col2", "Row3Col3", "Row3Col4"}
};
boolean recordFound = true;
int colIndex = 0;
while(recordFound) {
recordFound = false;
for(int row=0; row<twoDArray.length; row++) {
String[] rowArray = twoDArray[row];
if(colIndex < rowArray.length) {
System.out.println(rowArray[colIndex]);
recordFound = true;
}
}
colIndex++;
}
Output is:
Row1Col1
Row2Col1
Row3Col1
Row1Col2
Row2Col2
Row3Col2
Row1Col3
Row3Col3
Row3Col4
It's not a very "natural" thing to happen, due to the way Java arrays are nested and not rectangular multidimensional. For example, the following is possible:
[ ][ ][ ]
[ ][ ]
[ ][ ][ ][ ][ ]
where [ ] is an element.
Traversing this vertically is not a very "natural" or efficient operation. You could, however, do so by traversing columns up to the maximum of the array lengths, avoiding array out of bound issues with explicit checks or (being more evil) silently dropping ArrayOutOfBounds exceptions.
Edit: In the rectangular case just switch the two loops. It will not matter which row's length you use.
static void columnFirst(List<List<Integer>> matrix) {
int max = 0;
for (int i = 0; i < matrix.size(); i++) {
max = Math.max(max, matrix.get(i).size());
}
for (int i = 0; i < max; i++) {
for (int j = 0; j < matrix.size(); j++) {
if (matrix.get(j).size() > i)
System.out.print(matrix.get(j).get(i) + " ");
}
System.out.println();
}
}
Input array
{{1, 2, 3, 4, 5, 6},
{1, 2, 3},
{1, 2, 3, 4, 5},
{1},
{1, 2, 3, 4, 5, 6, 7, 8, 9}}
Output:
1 1 1 1 1
2 2 2 2
3 3 3 3
4 4 4
5 5 5
6 6
7
8
9
/*
Assume that the length of the col[0] will be the same for all cols.
Notice: that we are access salaries[j] for each iteration of j while
[i] same the same.
*/
public void printColsValues() {
for(int i = 0; i < array[0].length; i++) {
for(int j = 0; j < array.length; j ++) {
System.out.println(arr[j][i]);
}
}
}
