How to bin 2d data?
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Yeping Sun
el 6 de Ag. de 2016
Dear all,
I have a 2-dimension coordinate set (x,y) which contains 5000 points and I want to construct a 2d map to reflect the point density distribution. firstly I want to divide both of the ranges of the two coordinate sets (-3 to2 for x; and -2.5 to 3 for y) into like 37 bins,so there will be totally 37x37 bins. Then I want to assign each point into these bins.To do that I need to construct a indicator function δkij (k=1:5000; i=1:37; j=1:37) which denotes whether point k falls in bin (i,j): if point k falls into bin (i,j), then δkij=1, otherwiseδkij=0. Then the histogram at bin (i,j) is the sum of δkij (k=1:5000). At last I wish to plot a contour map or hotmap to show the hisrogram. How does matlab realize these computation?
All the best!
Yeping Sun
1 comentario
Azzi Abdelmalek
el 6 de Ag. de 2016
Your question is not clear, post a short example, give a brief explanation on what you want, then post the expected result
Respuesta aceptada
Image Analyst
el 6 de Ag. de 2016
Editada: Image Analyst
el 6 de Ag. de 2016
Try (the badly named) hist3() to construct a 2-D histogram:
% Create sample data.
numPoints = 5000;
x = -3 + 5 * rand(numPoints, 1);
y = -2.5 + 5.5 * rand(numPoints, 1);
% Now construct the histogram
xy = [x, y];
subplot(1,2,1);
hist3(xy, [37, 37]); % Plots bar chart.
subplot(1,2,2);
counts = hist3(xy, [37, 37]);
imshow(counts, []); % Show as image
colormap(hot(256));
colorbar;
axis on;
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/174827/image.png)
8 comentarios
Image Analyst
el 9 de Ag. de 2016
SOrry, I meant XData and YData, like this:
imshow(heatMap, 'XData', [-3 3], 'YData', [-3,3]);
but you should really use histogram2() and get the BinEdges property and use that instead of [-3, 3] because [-3,3] may not be correct if the histogram was automatic. However if you passed in the edges, then you know what the edges are and you can use that.
Más respuestas (2)
Steven Lord
el 6 de Ag. de 2016
Use the histogram2 function. The DisplayStyle 'tile' looks like it's exactly what you're looking for.
0 comentarios
Thorsten
el 9 de Ag. de 2016
Editada: Thorsten
el 9 de Ag. de 2016
Have a look at this:
D = dlmread('/Users/hansen/Downloads/PC1-PC2.txt');
Nbins = 37;
H = hist3(D, {linspace(-3,3,Nbins) linspace(-3,3,Nbins)});
imshow(H, [])
colormap hot
colorbar
The values of H are in the range [0, 196], and that is the range of the colorbar.
For a contour plot, use:
contour(H)
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