how to do density plot?
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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 个评论
Adam Danz
2018-9-19
This code writes data to your data.txt file. Option 1 is to read the file to get the data back into matlab and then do the plotting. Option 2 is to save the data within this function/script so you don't have to read it back in. Depending on what you're trying to do, you may not even need to write it to the txt file in the first place (option 3).
Secondly, you need to specify what data you want to plot. For example, do you want to plot the density of each column of T separately?
Thirdly, how would you like to represent the density? Are you looking to plot a histogram?
sourabh mittal
2018-9-19
编辑：sourabh mittal
2018-9-19
Adam Danz
2018-9-19
I continued in the answer section though I'm unsure about the plot you're describing.
sourabh mittal
2018-9-20
采纳的回答
Image Analyst
2018-9-19
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 个评论
sourabh mittal
2018-9-19
编辑：sourabh mittal
2018-9-19
Image Analyst
2018-9-19
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().
sourabh mittal
2018-9-20
更多回答（1 个）
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 个评论
Adam Danz
2018-9-19
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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