MATLAB: Using Matlab to plot density contour for scatter plot

density contour for scatter plot

Hi guys, I'm trying to use Matlab to plot the density contour for the following scatter plot. The bins will be 1X1 box. Within my limited understanding the density contour should be indicated how many points fall into the bins(correct me if I'm wrong), but I still cannot find a way to do the density plot. Need some help to solve this problem. Thanks!

Best Answer

Scatter doesn't do any binning. It's showing each individual data element.

Perhaps this approach does what you want?

x = randn(1,1000);
y = randn(1,1000);
n = hist3([x', y']);
pcolor(n)

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MATLAB: Use imagesc to plot data extracted from hist3

Be sure to read the documentation of imagesc. The first two inputs, if specified, are used to create the X and Y axes on the plot. However, the function uses ONLY the first and last element of each and linearly interpolates between them. Therefore, you got a linear scale from -1 to 7 for both dimensions. To fix this problem, the axis inputs to imagesc should really be generated directly from the output of hist3, so the bins in your images are identical to the bins from your histogram.

X = [-1 -5 3 6 -1 7];
Y = [-1 -6 3 6 -1 7];
[N,b] = hist3([X', Y'],[numel(X) numel(X)]); 
figure
imagesc(b{1}([1 end]),b{2}([1 end]),N);
colorbar
axis xy equal tight

Note that

axis xy
ensures that the Y axis points up. imagesc expects data in image ij format, which is why the histogram axis was upside down previously.

I also suspect you may want to more carefully define the bins for your histogram as right now the Y bins are slightly larger than your X bins. You should be able to figure this out from the documentation for hist3 if you'd like to change that.

Hope that helps!

MATLAB: Contour map from hist3()

Supply output variables to hist3:

 [n,c] = hist3(X, [10 10]);
 contour(c{1}, c{2}, n);

Best Answer

Related Solutions

MATLAB: Use imagesc to plot data extracted from hist3

MATLAB: Contour map from hist3()

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