MATLAB: Selecting numbers in matrix that are repeated

MATLABmatrixrepeatunique

I have a 60×5 matrix A and would like to find the answer vector that lists all the numbers in A that appeared at least 2 times/remove those numbers that only appeared once. How may I write for this?

(A contains some NaNs too)

Thank you! 🙂

Best Answer

Try this:

A = randi(1000, 60, 5);                                 % Create Matrix
[Au,~,ix] = unique(A,'stable');                         % Unique elements in ‘A’
tally = accumarray(ix,1);                               % Number Of Occurrences Of Each
keep = tally > 1;                                       % Keep Indices Of Occurrences > 1
out1 = [Au(keep), tally(keep)];                         % Display Numbers & Occurrences
Ai = ismember(A,out1(:,1));                             % Return Logical Index Of Occurrences > 1
Anew = A .* Ai;                                         % Matrix With ‘Single-Occurrence’ Elements Eliminated

The ‘Anew’ matrix has 0 values for the elements that are not repeated, those that are repeated appear in their expected locations.

If you only want the values of the numbers that aare repeated, and the number of repeats, those are contained in the ‘out1’ matrix.

Related Solutions

MATLAB: Determine indices of how many times (x,y) coordinates occur in 2d vector

Try this:

M = randi(5, 25, 2);                                                                                    % Create ‘LatLon’ Data
[Mu,~,idx] = unique(M, 'rows');                                                                         % Unique Rows
Tally = accumarray(idx, (1:numel(idx)).', [], @(x) {M(x,:)});                                           % Calculate Frequencies, Return Pairs By Group
pairs = cellfun(@(x)size(x,1), Tally);                                                                  % Recover ‘LatLon’ Pairs
idxc = accumarray(idx, (1:numel(idx)).', [], @(x) {x.'});                                               % Get Indices
idxmtx = zeros(numel(pairs),max(pairs(:)));                                                             % Create Matrix For Indices
for k = 1:size(idxmtx,1)
    idxmtx(k,1:pairs(k)) = [idxc{k}];                                                                   % Assign Indices To Appropriate Rows
end
[~,ixs] = sort(pairs, 'descend');                                                                       % Sort Them
Result = table(Mu(ixs,:),pairs(ixs),idxmtx(ixs,:), 'VariableNames',{'LatLon','Frequency','Indices'});   % Output Table Of Pairs & Frequencies
ResultSel = Result(pairs(ixs) > 1,:)                                                                    % Select Only Occurrences > 1

Substitute your coordinates for the ‘M’ matrix in my code.

If the coordinates are not exact, consider substituting uniquetol with the ByRows name-value pair for unique.

MATLAB: Finding frequency of values in an array

One approach:

negPhase = nnz(Phase < 0);                          % Number Of Values < 0
[uPhase,ia,ic] = unique(Phase);
tally = accumarray(ic, 1);
freqOccurrence = [uPhase, tally];                   % Frequency Of Occurrenct Of Each Value

If you do not want the results sorted (since the unique function does this by default), use:

[uPhase,ia,ic] = unique(Phase, 'stable');

instead. The rest of the code is unchanged. (Note that this will conform to the MATLAB linear matrix indexing convention, so it will be a column vector, not a matrix.)

Best Answer

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MATLAB: Determine indices of how many times (x,y) coordinates occur in 2d vector

MATLAB: Finding frequency of values in an array

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