Extract values common to 5 columns

Hi, I have a matrix A with 5 columns (1 to 5). I want to compare columns 1 through 5 and then extract values common to all 5 columns. Put the extracted values (common to all 5 columns) into a separate matrix called Match. Thank you!

[James Tursa]

What have you done so far? What specific problems are you having with your code?

[Curious Mind]

I have a code that solves this task if there are only 2 columns under consideration.

data = randi(3,12,4); NewMatch = data(:,2) == data(:,4); Print = data(NewMatch,:)

I want to extract common values in all 5 columns this time. The above code compares just 2 columns. Any thoughts?

[Star Strider]

Is this homework? If so we can only give hints.

If it is not homework, I will post my general solution.

[Curious Mind]

Not at all. Not a homework.

Answer 1

[Star Strider]

Since it is not homework, see if this does what you want:

A = randi(9,20,5);                                      % Create Matrix (Integers For Simplicity)
[Au,ia,ic] = unique(A);                                 % Unique Elements (Use ‘uniquetol’ For Non-Integers)
[~,c] = ind2sub(size(A), (1:numel(A)).');               % Create Vector Of Column Indices
Tally = accumarray(ic,c,[],@(x){Au(x)});                % Accumulate By Column
ColsWithAu = cellfun(@(x)nnz(ismember(Au,x)), Tally);   % Return Columns With Specific Elements
Common = Au(ColsWithAu==5)                              % If Element Appears In Every Column, It Is Common To All Columns

It worked for my test matrix.

If your rmatrix has floating-point elements, use uniquetol instead of unique. You will need to choose the appropriate tolerance value.

Answer 2

[James Tursa]

Hint: Look at the result of diff(A,[],2). If all the values in a row are equal, what would you expect to be in the result of this diff calculation? Can you devise a test base on this result to see if every value in a row is the same?