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

2016 2 6
1 个回答
更新时间：2016 2 7
8 次查看（30 天）

0 个投票

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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回答（1 个）

the cyclist
the cyclist 2016-2-6

1 个投票

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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Image Analyst
Image Analyst 2016-2-6
编辑：Image Analyst 2016-2-6
Cool, I didn't know about histcounts2(). I have the Statistics and Machine Learning Toolbox so I've been using the (in my opinion, poorly named) hist3() to compute 2D histograms.
dipak sanap
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
dipak sanap 2016-2-7
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

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