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Index › Programming Questions & Help › Syntax Questions › Populate a 2D array
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Populate a 2D array (Read 1044 times)
windym
Populate a 2D array
Jun 22nd, 2006, 10:59am  
Hi there,

I am trying to figure out how to specify values in a 2D array. So far I have this 1D array that stores a set of Vector coordinates:

Vector3D[]target1 = {new Vector3D(20,20), new Vector3D(50,20), new Vector3D(100,20)};

However, I'd really like to have e.g. 3 sets of coordinates in the array. In other words, an array with 3 indexes, each of which stores its own array.

My guess is that the syntax would start something like this:

Vector3D[][]targets = ???

Any help would be very much appreciated. I can't quite get my head around this multi-dimensional array stuff Sad

cheers,
Matt
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JohnG
Re: Populate a 2D array
Reply #1 - Jun 22nd, 2006, 11:04am  
If you really want to populate your array in that way, then the syntax is (I think)
Code:
type[][] foo={{type(0,0),type(0,1),type(0,2)}, {type(1,0),type(1,1),type(1,2)}, {type(2,0),type(2,1),type(2,2)}};


However that's really ick.
It's probabyl betyter to do something like:

Code:
type[][] foo=new type[3][3];
type[0][0]=new type(0,0);
type[0][1]=new type(0,1);
type[0][2]=new type(0,2);
type[1][0]=new type(1,0);
type[1][1]=new type(1,1);
type[1][2]=new type(1,2);
type[2][0]=new type(2,0);
type[2][1]=new type(2,1);
type[2][1]=new type(2,2);

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windym
Re: Populate a 2D array
Reply #2 - Jun 22nd, 2006, 11:27am  
That helps a lot. Many thanks.
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windym
Re: Populate a 2D array
Reply #3 - Jun 22nd, 2006, 11:55am  
I was just wondering, does anyone happen to have any idea of how I could then randonly select from the 2D array? I need to take a random set of coordinates.

The original code for my 1D array was like this:

// store values in array
Vector3D[]target = {new Vector3D(20,20), new Vector3D(50,20), new Vector3D(100,20)}

// a function that returns a random index from that array:
Vector3D someTarget() {
 return target[int(random(target.length))];
}

//use that function to store a target position (that my Boid object moves to)
Vector3D goodTarget = someTarget();

Now that I have a 2D array, how do I change the function above to select an array of Vector objects rather than a single object as before?

My head hurts!
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JohnG
Re: Populate a 2D array
Reply #4 - Jun 22nd, 2006, 2:41pm  
Code:
// a function that returns an array from a random index 
// from that array:
Vector3D[] someTarget() {
  return target[int(random(target.length))];
}

Vector3D[] goodTarget = someTarget();


Or to chose a single thing from a 2D array
Code:
Vector3D someTarget() {
  int i=int(random(target.length));
  int j=int(random(target[i].length));
  return target[i][j];
}

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windym
Re: Populate a 2D array
Reply #5 - Jun 22nd, 2006, 4:37pm  
That seems to work perfectly. Thanks again - you're a star!

Matt Wink
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windym
Re: Populate a 2D array
Reply #6 - Jun 22nd, 2006, 5:39pm  
OK so that all seems to work well. I've figured out that if I use the following code inside the function, I can refer to a specific set of my co-ordinates:

Vector3D[] someTarget() {
 return target[4];
}

So I have a one final question (I promise!):

What would be ideal would be for the function to return a specific array depending on which key is pressed. The problem is, as soon as I put any keypress or if/else statements inside the function, it returns an error. Here is my poor attempt at the code:

Vector3D[] someTarget() {

 if(keyPressed) {
   if (key == 'a' || key == 'A') {
     return target[0];
   }

   if (key == 'b' || key == 'B') {
     return target[1];
   }



 }
}

It tells me that the function "must return an expression compatible with type Vector3D[]"

As you must have guessed I'm a complete novice when it comes to programming. Is my syntax completely wrong?
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Ira
Re: Populate a 2D array
Reply #7 - Jun 22nd, 2006, 6:43pm  
When a function has a return type other than void, the function needs to return that type. Nesting return statements within other blocks (your conditionals) doesn't ensure that (from the compiler's perspective.)

Here's a more structured verson of what I think you're trying to do.
Code:

Vector3D[]target = { new Vector3D(1,2,3), new Vector3D(4,5,6) };
Vector3D w = new Vector3D();

void draw(){
}

Vector3D getTarget() {
  println("target = ("+w.x+", "+w.y+", "+w.z+")");
  return w;
} 

void setTarget(Vector3D w) {
  this.w = w;
} 

class Vector3D{
  float x, y, z;
  Vector3D(float x, float y, float z){
    this.x = x;
    this.y = y;
    this.z = z;
  }
  
  Vector3D(){
  }
}

void keyPressed() {
  if (key == 'a' || key == 'A') {
    setTarget(target[0]);
  } 
  else if (key == 'b' || key == 'B') {
    setTarget(target[1]);
  }
  getTarget();
}
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windym
Re: Populate a 2D array
Reply #8 - Jun 22nd, 2006, 6:58pm  
Great thanks. I'll take a look at your code and see if I can get my head around it.

cheers,
Matt
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Ira
Re: Populate a 2D array
Reply #9 - Jun 22nd, 2006, 7:32pm  
Matt,
One other clarification, which may not be obvious in my code, you wouldn't really want to call getTarget() from within the keyPressed() function. I just did that so you could see the output. You'd likely want to create another function (which called getTarget()) that actually used or assigned the returned Vector3D obj.

ira
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Processing: Creative Coding and Computational Art
http://friendsofed.com/book.html?isbn=159059617X

The Essential Guide to Processing for Flash Developers
http://www.friendsofed.com/book.html?isbn=9781430219798

Center of Creative Computation
Meadows/Lyle
SMU, Dallas
WWW irarobinian  
windym
Re: Populate a 2D array
Reply #10 - Jun 22nd, 2006, 7:57pm  
Thanks Ira. I must say that I'm finding it quite hard to adapt what you've done to my code but I will persevere! Wink
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Ira
Re: Populate a 2D array
Reply #11 - Jun 22nd, 2006, 9:01pm  
Sorry for the trouble;-)
In the long run it's beneficial to organize code as smallish, concise and hopefully reusable structures; it's also good practice as you delve deeper into OOP.

Learning this stuff is all about perseverance – a point I struggle to instill in my students.
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Processing: Creative Coding and Computational Art
http://friendsofed.com/book.html?isbn=159059617X

The Essential Guide to Processing for Flash Developers
http://www.friendsofed.com/book.html?isbn=9781430219798

Center of Creative Computation
Meadows/Lyle
SMU, Dallas
WWW irarobinian  
windym
Re: Populate a 2D array
Reply #12 - Jun 23rd, 2006, 3:53pm  
Finally got it to work! What a relief. Thanks for the help everyone. Very much appreciated Smiley
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