How to append to a 2 dimensional array?

Processing Coding Questions
1

Hello, I’m having trouble finding an answer to this problem.

  1. How would you append an array to an array.

One of the ways I have tried doing this:

int[][] array;

  for (int i=1; i<=20; i++) { 
      append(array,{0,0,0});
    }
 }
  1. How would you append to an array that was within that array?

How I’ve tried this:

int[][] array;

for (int i=1; i<=20; i++) { 
    for (int j=1; j<=20; i++) {
      append(array[i][j],0);
    }
 }

Thanks in advance.

1 Like
2

i play long ago, and sure there are better ways

array copy expand 
// array expand test
// https://processing.org/discourse/beta/num_1175740933.html
int[][] test ={{11, 12, 13}, {21, 22, 23}, {31, 32, 33}, {41, 42, 43}};
int[][] tmp ;
int cols1,rows1,cols2,rows2;

cols1=test[0].length;
println(" test[0].length == columns : "+cols1);
rows1=test.length;
println(" test.length == rows : "+rows1);

for (int i = 0; i<4; i++) {
  for (int k = 0; k<3; k++) {
    println("row ["+i+"] "+" col ["+k+"] : "+test[i][k]);
  }
}

// backup
tmp = new int[rows1][cols1];
println(" copy to tmp ");
tmp = test;
for (int i = 0; i<4; i++) {
  for (int k = 0; k<3; k++) {
    //println("row ["+i+"] "+" col ["+k+"] : "+tmp[i][k]);
  }
}

// expand:
println(" make one longer ");
test = new int[rows1+1][cols1];

cols2=test[0].length;
println(" test[0].length == columns : "+cols2);
rows2=test.length;
println(" test.length == rows : "+rows2);
for (int i = 0; i<rows2; i++) {
  for (int k = 0; k<cols2; k++) {
    //println("row ["+i+"] "+" col ["+k+"] : "+test[i][k]);
  }
}
println(" copy back ");
for (int i = 0; i<rows1; i++) {
  for (int k = 0; k<cols1; k++) {
    test[i][k] = tmp[i][k];
    //println("row ["+i+"] "+" col ["+k+"] : "+test[i][k]);
  }
}
println(" show all ");
for (int i = 0; i<rows2; i++) {
  for (int k = 0; k<cols2; k++) {
    println("row ["+i+"] "+" col ["+k+"] : "+test[i][k]);
  }
}

that might be a good reason to make a class and a arrayList of it?

class Row {
  int x,y;
  Row(int _x, int _y ) {
    x=_x;
    y=_y;
  }
}

ArrayList<Row> my_array = new ArrayList<Row>();

void setup(){
  my_array.add( new Row(1,2) );
  my_array.add( new Row(3,4) );
  for ( int i = 0;i < my_array.size();i++) println(my_array.get(i).x , my_array.get(i).y );
}

but a much better reason for it is that you can make mixed record types with it,
just add string, float, boolean variables to the class…

1 Like
3

Its a lot more typing but ArrayList is better for performance if you plan on doing this a lot. The disadvantage is you can’t use primitive data types only the class wrappers which are slower. The advantage of using ArrayList instead of append is it doesn’t have to create a new array every time you add something to it.

// initialization
ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();

// append to array list that is already in the 2d list
list.get(/* index */).add(/* value */);

// append a new arraylist to the 2d list
ArrayList<Integer> otherList = new ArrayList<Integer>();
otherList.add(5);
list.add(otherList); // you can either create an otherList object
list.add(new ArrayList<Integer>()); // or add an empty one

// add the contents of one 2d list to the end of another
ArrayList<ArrayList<Integer>> other2d = new ArrayList<ArrayList<Interger>>();
list.addAll(other2d);
2 Likes
4

I am doing this just in setup(), but need to refer back to variables from these arrays/ArrayLists in draw(). Would it still be faster to use ArrayList or just an array?

If an array is faster, how would you code that?

5

sorry that is little bit hidden under the above

array copy expand

link you might have missed

array list use array in a smart way, so on some scale it might be slower…
tell me when you notice it.

the thinking/using array .vs. arraylist
has to do with the available functions
you might get a idea here from the intList

using array and make some better code ( like put / use it as a own function )
might have same result, still it not easy beats this line:
my_array.add( new Row(a,b) );

as i define the arrayList “my_array” global, you can use it in setup ( and draw )
if you move that line down into setup it will be NOT usable further.
now i not see further considerations for that but there can be.

1 Like
6

If that’s so, it means you already know how many rows & columns your 2D array is gonna need. :flushed:

Apparently, according to your posted double loop example, that 2D array is 20 x 20. :nerd_face:

So you’re just gonna need this, and you’re done: :bulb:

static final int ROWS = 20, COLS = 20;
final int[][] grid = new int[ROWS][COLS];

void setup() {
  for (final int[] row : grid)  println(str(row));
  exit();
}
3 Likes