Best to represent two large data sets in one plot

Hi everyone,

I am dealing with a scatter plot on which I'd like to plot two data sets containing at least 1500 dots per dataset. This number can reach 10000.

So far I am plotting those points by using a scatter plot:

Do you think Matlab offers a better way to show my data?

Thank you, Flo

Answer 1

[Image Analyst]

Depends on what you want to do or show. One option is you could create an image where you put one set into the red channel and one into the blue channel. Then you could increment a pixel to make it brighter when you happen to have multiple data values with the same x,y location. It will also let you see both sets at the same time (overlaps will be purplish) instead of the blue set, which you plotted last, covering up and totally obscuring the red data.

[Flo]

Interesting way of doing it. I will try to find out how to do that. thank you

[Image Analyst]

Try to adapt this:

fontSize = 15;

numPoints1 = 5000;
set1x = rand(numPoints1, 1);
set1y = 25 * rand(numPoints1, 1);

numPoints2 = 4000;
set2x = rand(numPoints2, 1);
set2y = 25 * rand(numPoints2, 1);

subplot(2, 2, 1);
plot(set1x, set1y, 'r.');
hold on; 
plot(set2x, set2y, 'b.');
grid on;
title('Scatterplot', 'FontSize', fontSize);

% Make an image
rows = 300;
columns = 400;
redChannel = zeros(rows, columns);
blueChannel = zeros(rows, columns);
maxX1 = max(set1x);
maxY1 = max(set1y);
maxX2 = max(set2x);
maxY2 = max(set2y);
% Assign set 1 to red channel
for k = 1 : numPoints1
  thisX = round(set1x(k) * columns / maxX1);
  thisY = round(set1y(k) * rows / maxY1);
  if thisX < 1
    thisX = 1;
  end;
  if thisY < 1
    thisY = 1;
  end;
  redChannel(thisY, thisX) = redChannel(thisY, thisX) + 1;
end
subplot(2,2,2);
imshow(redChannel, []);
title('Set 1', 'FontSize', fontSize);

% Assign set 2 to blue channel
for k = 1 : numPoints2
  thisX = round(set2x(k) * columns / maxX2);
  thisY = round(set2y(k) * rows / maxY2);
  if thisX < 1
    thisX = 1;
  end;
  if thisY < 1
    thisY = 1;
  end;
  blueChannel(thisY, thisX) = blueChannel(thisY, thisX) + 1;
end
subplot(2,2,3);
imshow(blueChannel, []);
title('Set 2', 'FontSize', fontSize);

% Make RGB image
rgbImage = cat(3, mat2gray(redChannel), zeros(rows, columns), mat2gray(blueChannel));
subplot(2,2,4);
imshow(rgbImage, []);
title('both in an RGB image', 'FontSize', fontSize);