Kernel Density for 2D data

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Devinya Herath 2011-10-15

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评论： Joseph Byrnes 2022-4-19

I have two series of data(both of type double). I want to generate a kernel density plot from these. Pls help. My coding is given below.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
curs1 = exec(conn, 'select sp_x, sp_y from road_part6_trajectories_oneway2_new_segments_cartesian2');
format long;
curs1 = fetch(curs1);
AA = curs1.Data;
x = [AA{:,1}]';
y = [AA{:,2}]';
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

I want to generate the kernel density or any other suitable density plot for x and y. pls advise.

采纳的回答

the cyclist 2011-10-15

5
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The function ksdensity() will do kernel density estimation. It's not clear to me what your x and y represent, so it's hard to give more specific advice than that.

In response to comments, here is some code with an example of 2-d kernel density estimation, with a plot of the results. Important note: this assumes that x and y are independent from each other.

% Generate some normally distributed data
x = randn(50,1);
y = randn(50,1);
% Estimate a continuous pdf from the discrete data
[pdfx xi]= ksdensity(x);
[pdfy yi]= ksdensity(y);
% Create 2-d grid of coordinates and function values, suitable for 3-d plotting
[xxi,yyi]     = meshgrid(xi,yi);
[pdfxx,pdfyy] = meshgrid(pdfx,pdfy);
% Calculate combined pdf, under assumption of independence
pdfxy = pdfxx.*pdfyy; 
% Plot the results
mesh(xxi,yyi,pdfxy)
set(gca,'XLim',[min(xi) max(xi)])
set(gca,'YLim',[min(yi) max(yi)])

yes. that's right. I want to plot the 2-d frequency distribution. I have plot the histogram (using hist3) but I want a plot which clearly shows the dense areas. I initially thought that a kernel density would be suitable for this

Bjorn Gustavsson 2011-10-24

Then you should start with a two-dimensional histogram. There are several contributions with such tools on the file exchange. To use the cyclist's code you have to show that the variables are independent. A quick look with a 2-D histogram will help you get a look of that.

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