MATLAB: Most frequent value in a 3D matrix other than 0

frequent value

Dear all

I have got a 3D matrix, say A ( 100 by 100 by 20) containing elements of '0' , '1' , '2', '3', '4'.

I would like to know which elements happens the most frequent, except for '0'. My idea is to reshape the matrix to a vector using

A=reshape(A,100*100*20,1);
numbers = unique(A);   % sorted occurrence 
count=hist(A,numbers);
pointer = find(count == max(count(2:end))); % by using (2:end), I excluded the effect by '0'
value = numbers(pointer);

However, this seems redundant, any one have a better way to do that? Say, dealing with the 3D matrix straight. My 3D matrix will be very large….

Best

Yuan Chen

Best Answer

A=randi([0 4],100,100,20); %Example
[freq,number]=max(histc(A(:),1:4))

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MATLAB: How to get the program to display the most and least Freq used words? Tells me the # times used but I dont know how to get it to display the words. PLease Help!

The easiest way to do this is with accumarray:

a = fileread('GreatExpectations.txt');
w = regexpi(a, ' ', 'split');
[v,~,ic] = unique(w);
counts = accumarray(ic, 1);
imx = find(counts == max(counts));
imn = find(counts == min(counts));
fprintf(1,'\n\tMost frequent: “%s” appears %d times\n', v{imx}, counts(imx))
fprintf(1,'\n\tThere are %d that only appear one time\n\n', length(imn))

I used find rather than the second output of max and min because they only return the first index of the occurrence of the maximum or minimun while find returns them all.

The code produces:

  Most frequent: “the” appears 25 times
  There are 188 that only appear one time

MATLAB: How to find index of duplicate values in a matrix

Your example output (a 3x2 cell array) can only work if the numbers of repeat is the same for all repeated values. Otherwise you'll need a cell array of cell array. Furthermore, in general it's not a good idea to keep a [row, column] pair of indices, a linear index is more usually more useful.

Here is how I'd go about obtaining something similar to your desired output, that works regardless of the number of repeats:

A = [1 2 3 ; 4 2 3];
[uvalues, ~, uid] = unique(A(:));  
count = accumarray(uid, 1);   %easiest way to calculate the histogram of uvalues

linindices = accumarray(uid, (1:numel(A))', [], @(idx) {idx});  %split linear indices according to uid
valwhere = [num2cell(uvalues), linindices];  %concatenate
valwhere(count == 1, :) = []    %remove count of 1

The above gives you the list of linear indices. If you do really want the (row, column pairs):

A = [1 2 3 ; 4 2 3];
[uvalues, ~, uid] = unique(A(:));  
count = accumarray(uid, 1);   %easiest way to calculate the histogram of uvalues
[rows, cols] = ind2sub(size(A), (1:numel(A))');
rowcols = accumarray(uid, (1:numel(A))', [], @(idx) {num2cell([rows(idx), cols(idx)], 2)'});
valwhere = [num2cell(uvalues), rowcols];
valwhere(count == 1, :) = []

Best Answer

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MATLAB: How to get the program to display the most and least Freq used words? Tells me the # times used but I dont know how to get it to display the words. PLease Help!

MATLAB: How to find index of duplicate values in a matrix

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