MATLAB: How to find rows with multiple entries that are equal

logical indexing; find; rows; ismember; any; all;MATLAB

I have a NxM matrix and I want to find the rows that have M-1 duplicate entries. For example:
A=[1 1 2 4;
   2 2 2 1;
   2 9 3 0;
   3 0 3 3;
   4 3 2 2];
fun(A);
ans = [2 2 2 1;
       3 0 3 3]
How could I do this, preferably elegantly in a few lines? I am trying to avoid loops because I anticipate working with large matrices eventually.

Best Answer

In two lines:
sA=sort(A,2);
A(sum(sA(:,2:end)==sA(:,1:end-1),2)==size(sA,2)-2,:)
  ans =
     2     2     2     1
     3     0     3     3
Here's another method that doesn't use sort(). It's slightly faster for large matrices on my machine:
rowIdx=(sum(repmat(A(:,1),1,size(A,2))~=A,2)==1) | ...
    (sum(repmat(A(:,2),1,size(A,2))~=A,2)==1);
A=A(rowIdx,:);
You might want to break that down into more lines of code for readability.
Hope this helps.
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