How can I create points, display them and store them in some sort of Array

Question

I want to create points and then store them in an array. I'm doing this to put a linear regression through my data points afterwards. So I need to be able to cycle through all my points.

I could not find anything like that on the web for processing and as I was not really able to do it, I need your help. Here is my approach, but it doesn't seem to work:

ArrayList<dataPoint> dataPoints = new ArrayList<dataPoint>();

void setup(){
  size(1000, 1000); 
  background(255);
}
void draw(){
  for (int i = 1; i == dataPoints.size(); i++) { 
    // An ArrayList doesn't know what it is storing so we have to cast the object coming out
    dataPoint Point = dataPoints.get(i);
    Point.display();

  }  
}

void mousePressed() {
  dataPoints.add(new dataPoint(mouseX, mouseY));
}

class dataPoint {

  float x;
  float y;

  dataPoint(int tempX, int tempY) {
    x = tempX;
    y = tempY;
  }

  void display() {
    strokeWeight(10);
    stroke(255,0,0);
    point(x,y);
  }
}

I would like to have a program to create points and store them in an array (or something similar, that you can cycle through).

Can you please be more specific? What do you mean when you say this doesn't work? What did you expect the code to do? What did it do instead? — Kevin Workman, May 13 '19 at 15:18

George Profenza · Accepted Answer · 2019-07-17T11:28:41.177

Most of your code makes sense, there are only two gotchas I could spot that may prevent you from cycling through all your points and visualising them:

your condition is will go to an array index out of bounds: try for (int i = 0; i < dataPoints.size(); i++)
remember to clear the frame, otherwise you're drawing on top of the same dots over and over again

Remember array indices start at 0 in Processing/Java (and likewise the last index will not be the size() of your array, but the 1 less, hence the < in the for condition)

Here is your code with the above tweaks:

ArrayList<dataPoint> dataPoints = new ArrayList<dataPoint>();

void setup(){
  size(1000, 1000); 


}
void draw(){
  background(255);
  for (int i = 0; i < dataPoints.size(); i++) { 
    // An ArrayList doesn't know what it is storing so we have to cast the object coming out
    dataPoint Point = dataPoints.get(i);
    Point.display();

  }  
}

void mousePressed() {
  dataPoints.add(new dataPoint(mouseX, mouseY));
}

class dataPoint {

  float x;
  float y;

  dataPoint(int tempX, int tempY) {
    x = tempX;
    y = tempY;
  }

  void display() {
    strokeWeight(10);
    stroke(255,0,0);
    point(x,y);
  }
}

Note that Processing has a handy PVector class (which has x,y properties) so you could do something like this:

ArrayList<PVector> dataPoints = new ArrayList<PVector>();

void setup(){
  size(1000, 1000); 
  strokeWeight(10);
  stroke(255,0,0);
  noFill();
}
void draw(){
  background(255);
  beginShape();
  for (int i = 0; i < dataPoints.size(); i++) { 
    PVector point = dataPoints.get(i);
    vertex(point.x,point.y);
  }  
  endShape();
}

void mousePressed() {
  dataPoints.add(new PVector(mouseX, mouseY));
}

This a bit of a detail, but I recommend to following Java Naming Convention to keep the code consistent. (For example: renaming the dataPoint class to DataPoint and renaming the Point instance to point)

How can I create points, display them and store them in some sort of Array

1 Answers1