How to find the frequency of each row with certain coordiante in a matrix?

Question

Mnr 2014-3-29

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https://ww2.mathworks.cn/matlabcentral/answers/123631-how-to-find-the-frequency-of-each-row-with-certain-coordiante-in-a-matrix

回答： Aditya Rathore 2022-2-1

Hello all,

I have an mx2 matrix with its rows (0,1), (-1,0), (0,1), (0,-1), (1,1), (-1,1), (1,-1),(-1,-1); I would like to find the frequency of each of above coordinates. In other words, if I have A=[1 1;0 1;-1 1;1 0;-1 1], I would like to get something like,

number of times that (1,1) has appeared=1; number of times that (0,1) has appeared=1; number of times that (-1,1) has appeared=2; number of times that (1,0) has appeared=1; number of times that (0,-1) has appeared=0; number of times that (-1,-1) has appeared=0; number of times that (-1,0) has appeared=0; number of times that (1,-1) has appeared=0;

when I use "find" command I get an error. Thank you.

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Answer 1

Azzi Abdelmalek 2014-3-29

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https://ww2.mathworks.cn/matlabcentral/answers/123631-how-to-find-the-frequency-of-each-row-with-certain-coordiante-in-a-matrix#answer_131265

编辑：Azzi Abdelmalek 2014-3-29

在 MATLAB Online 中打开

A=[1 1; 0 1; 1 0; -1 1;-1 1;0 1;0 1]
[ii,jj,kk]=unique(A,'rows','stable')
f=histc(kk,1:numel(jj)); % Frequency
result=[ii f]

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Azzi Abdelmalek 2014-3-29

编辑：Azzi Abdelmalek 2014-3-29

在 MATLAB Online 中打开

Ok use this (without stable option), maybe you have an old version of Matlab

A=[1 1; 0 1; 1 0; -1 1;-1 1;0 1;0 1]
[ii,jj,kk]=unique(A,'rows')
f=histc(kk,1:numel(jj)); % Frequency
result=[ii f]

Mnr 2014-3-29

Thank you so much! I really appreciate your help!

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Answer 2

Aditya Rathore 2022-2-1

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https://ww2.mathworks.cn/matlabcentral/answers/123631-how-to-find-the-frequency-of-each-row-with-certain-coordiante-in-a-matrix#answer_886060

在 MATLAB Online 中打开

There are two things:

Your row length is small (2)
You want to also retrieve the stored values

I suggest you make a matrix for storing frequencies

freqs = zeros(m, 2);
[rows, ~] = size(A);
for idx=1:rows
    i = A(idx, 1);
    j = A(idx, 2);
    freqs(i+2,j+2) = freqs(i+2, j+2) + 1; %Because you have -1 also
end