how to do density plot?
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sourabh mittal
on 19 Sep 2018
Commented: sourabh mittal
on 20 Sep 2018
suppose, I have a text file 'data.txt' that has three columns and contains output of below.
% code
fileID = fopen('data.txt','w');
for x = 0.1:0.1:10
for y = 0.1:0.1:10
z = x*y;
T = [x, y, z];
fprintf(fileID,'%f %f %f\n',T);
end
end
fclose(fileID);
Now i want to do the density plot of this data. Please help.
4 Comments
Adam Danz
on 19 Sep 2018
I continued in the answer section though I'm unsure about the plot you're describing.
Accepted Answer
Image Analyst
on 19 Sep 2018
Try this vectorized approach with meshgrid():
% Generate the data.
xv = 0.1:0.1:10
yv = 0.1:0.1:10
[x, y] = meshgrid(xv, yv)
z = x .* y
T = [x(:), y(:), z(:)]
% Show the x,y,z data as a surface
surf(xv, yv, z, 'EdgeColor', 'none');
xlabel('x', 'FontSize', 20);
ylabel('y', 'FontSize', 20);
zlabel('z', 'FontSize', 20);
% Write the file.
filename = fullfile(pwd, 'data.txt');
fileID = fopen(filename, 'wt');
fprintf(fileID,'%f %f %f\n',T'); % Don't forget to transpose with '
fclose(fileID);
type(filename);
% delete(filename);
3 Comments
Image Analyst
on 19 Sep 2018
OK. I thought you were going to visualize the data in the same program that created it. But it looks like Adam alerted you to the function dlmread(). But you might still look at my vectorized way of using meshgrid() - it's a handy function that allows you to do in one line what would otherwise be a multi line set of nested for loops.
Anyway, after calling dlmread(), you can use surf() like I showed, or scatter() or imagesc() like Adam showed, or even histogram() or histogram2(), depending on what you mean by density. Still even now, no one has a clear idea of what you mean by that, other than your acceptances of Adam's answer which I guess means you wanted either scatter() or imagesc().
More Answers (1)
Adam Danz
on 19 Sep 2018
Edited: Adam Danz
on 19 Sep 2018
You can read the data back in with dmlread()
data = dlmread('data.txt', '%f');
' data' will be the [10000 x 3] matrix.
For the figure, I'm not sure if this is what you're looking for but you can try it.
figure;
imagesc(data(:,1), data(:,2), data(:,3));
colorbar
Another option
figure;
scatter(data(:,1), data(:,2), 10, data(:,3))
1 Comment
Adam Danz
on 19 Sep 2018
See comments under the answer provided by @ImageAnalyst for more interpretations of what you'd like to plot in 2D space.
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