Counts in bins for 2D histogrsm using nested for loop ?

Question

dipak sanap 2016-2-6

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/266872-counts-in-bins-for-2d-histogrsm-using-nested-for-loop

评论： dipak sanap 2016-2-7

 I am trying to write extend 1D histogram code to 2D histogram, after creating bins using mesh grid
 how to count if data point x,y is in the bin?    
 %1D code
 A = [1 ;1 ;2 ;2 ;2 ;4 ;4 ;4 ;4 ;4 ;4 ;5 ;5 ;6 ;1 ];
 A_u = unique(A);
 z = zeros(size(A_u));
 for i = 1:length(A_u)
    z(i) = sum(A_u(i)==A); %Counts the frequency, need something similar for 2D
 end
 z = [A_u, z];
 %2D code
 x = [1,2,5,6,7,3,4,9,5,2,8]';
 y = [1,1,3,6,4,3,6,5,8,7,4]';
 xy = [x,y];
 mn_x = min(x);
 mx_x = max(x);
 mn_y = min(y);
 mx_y = max(y);
 x_rng = linspace(mn_x,mx_x,3);
 y_rng = linspace(mx_y,mn_y,3);
 [p,q] = meshgrid(x_rng,y_rng);
 z = zeros(size(p,1),size(q,2));
 for i = 1:size(p,1)
    for j = 1:size(q,2)
         %Need help here to decide criteria, like 1D histogram,
         problem is I  cant access all elements of xy as counters for loops goes
         through rows and columns of p and q. 
        z(i,j) = sum( (p(i) < xy(:,1) < p(i+1,:)) & (q(j) < xy(:,2) < q(j+1,:)) ); 
    end    
 end

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Answer 1

the cyclist 2016-2-6

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/266872-counts-in-bins-for-2d-histogrsm-using-nested-for-loop#answer_208773

在 MATLAB Online 中打开

If you have a relatively recent version of MATLAB, you could have gotten the 1-d counts using the histcounts command:

A = [1 ;1 ;2 ;2 ;2 ;4 ;4 ;4 ;4 ;4 ;4 ;5 ;5 ;6 ;1 ];
A_u = unique(A);
z = histcounts(A,[A_u; Inf]);

and you can get the 2-d counts using the histcounts2 command:

x = [1,2,5,6,7,3,4,9,5,2,8]';
y = [1,1,3,6,4,3,6,5,8,7,4]';
x_u = unique(x);
y_u = unique(y);
z2 = histcounts2(x,y,[x_u; Inf],[y_u; Inf])

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dipak sanap 2016-2-6

Well thanks for the reply. I am aware of these bin counting functions but my task is not to use in built function. Thats why I have to manually create a grid and then count frequency of each bins. Any help regarding nested loop which I have wriiten would be appreciated.

dipak sanap 2016-2-7

在 MATLAB Online 中打开

 Hey, I got it. I created a 2D meahgrid and counted frequency 
 in  each bin using inpolygon function. here is complete code.
 %x = input which I read from my data file.
 %y = input which I read from my data file.
 N = 401;
 mn_x = min(x);
 mx_x = max(x);
 mn_y = min(y);
 mx_y = max(y);
 x_rng = linspace(mn_x,mx_x,N);
 y_rng = linspace(mx_y,mn_y,N);
 [p,q] = meshgrid(x_rng,y_rng);
 z = zeros(size(p,1)-1,size(q,2)-1);
 for i = 1:size(p,1)-1
    for j = 1:size(q,2)-1
        xv = [p(i,j),p(i,j+1),p(i,j+1),p(i,j),p(i,j)];
        yv = [q(i+1),q(i+1),q(i,j),q(i,j),q(i+1)];
        in = inpolygon(x,y,xv,yv);
        z(i,j) = numel(x(in));
    end    
 end