# Selecting numbers in matrix that are repeated

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Charms 2019 年 12 月 1 日
Commented: Star Strider 2019 年 12 月 1 日
I have a 60x5 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! :)

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Star Strider 2019 年 12 月 1 日
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.

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Charms 2019 年 12 月 1 日
thank you! :) appreciate it
Star Strider 2019 年 12 月 1 日
As always, my pleasure!

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KALYAN ACHARJYA 2019 年 12 月 1 日
[N,edges]=histcounts(A,unique(A))
result_array=edges(N>1)

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Charms 2019 年 12 月 1 日
there seems to be an error using histcounts (needs to be monotonically increasingly) - had a similar code with you too :) thank you nonetheless kalyan!

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