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Counting frequency of occurrence in matrix

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Guan Zhao
Guan Zhao 2012-10-23
评论： Brian Derstine 2021-8-31
Good day,
I am attempting to count the number of times each number in a matrix occurred in the matrix.
For example, suppose I have a matrix;
x =
22 23 24 23
24 23 24 22
22 23 23 23
I want an output which will tell me 22 occurred 3 times, 23 occurred 6 times, and 24 occurred 2 times. The actual matrix is larger in size.
Is there a specific function which returns such values or are there any other ways I can resolve this challenge?
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Jerry Olup
Jerry Olup 2017-6-20
Let x be your vector. Something like this can save you an unnecessary toolbox:
xx = unique(x); % temp vector of vals
x = sort(x); % sorted input aligns with temp (lowest to highest)
t = zeros(size(xx)); % vector for freqs
% frequency for each value
for i = 1:length(xx)
t(i) = sum(x == xx(i));
end
Then the t vector shows freqs of the sorted, unique vector x.
m_vdv
m_vdv 2018-5-10
Hi, is it also possible to do this without using 'unique' and 'sort'? For example with only using a for loop and/or if loop? Thanks in advance.

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2012-10-23
x =[
22 23 24 23
24 23 24 22
22 23 23 23];
a = unique(x);
out = [a,histc(x(:),a)];
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Brian Derstine
Brian Derstine 2021-8-31
would be nice if you could just do tabulate(x)

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更多回答（3 个）

Aurelien Queffurust
Aurelien Queffurust 2012-10-23
Using nnz for example:
nnz(x==22)
will return 3
  1 个评论
Guan Zhao
Guan Zhao 2012-10-23
Hi,
My actual matrix will have at least 256 elements. I will have to consider zero elements too.
Regards
Guan Zhao

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Thomas
Thomas 2012-10-23
x=[22 23 24 23
24 23 24 22
22 23 23 23];
[a,b]=hist(x,unique(x));
out=[b' sum((a),2)]
abdelrahim hashem
abdelrahim hashem 2017-11-15
x = [22 23 24 23; 24 23 24 22; 22 23 23 23];
un_x = unique(x);
for i = 1:length(un)
un(i), length(find(x == un_x(i)))
end

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