How do i find rows that contain duplicate values only?

 for example i want to identify the row and column that contain "3" only and delete them from the data  

 x = [1 3 5 6; 2 3 6 4; 9 3 9 6; 3 3 3 3]

Answer 1

[OCDER]

x = [1 3 5 6; 2 3 6 4; 9 3 9 6; 3 3 3 3; 1 3 3 4]
B = (x == 3);
DelCol = sum(B, 1) == size(B, 1);
DelRow = sum(B, 2) == size(B, 2);
x(:, DelCol) = [];
x(DelRow, :) = [];

[flemingtb]

This works but i'm struggling to understand why. Can you explain the code in line '3' and '4'?

[OCDER]

This method uses logical indexing. https://www.mathworks.com/help/matlab/math/matrix-indexing.html

B = (x == 3) returns a matrix. 1 is where x == 3

   0   1   0   0
   0   1   0   0
   0   1   0   0
   1   1   1   1
   0   1   1   0

DelCol = sum(B, 1) == size(B, 1); Takes the sum of B downward along the row, then finds where the sum == the number of rows. 
                                  EX: If there are 5 3's and 5 rows, then that column is all 3's.

   0   1   0   0  

DelRow = sum(B, 2) == size(B, 2); same as above, but this find which rows are all 3's.

   0
   0
   0
   1
   0  

x(:, DelCol) = []; %Delete all columns where DelCol is 1
x(DelRow, :) = []; %Delete all rows where DelRow is 1