How can already used elements be eliminated one by one in 2D matrix while moving upwards? | Efficienlty

Input

input = [1 2 0;
         2 3 4;
         4 5 6];

Output

Output= [1 0 0;
         2 3 0;
         4 5 6];

Why efficiently : For inputting a big matrix of say 360000 x 36.

Answer 1

[James Tursa]

r = rot90(inputMatrix,-1); % turn rows into columns with last row as first column
[~,ix] = unique(r); % get the unique linear indexing with preference to leftmost columns
result = zeros(size(r)); % initialize result as all 0's
result(ix) = r(ix); % fill in the unique values with preference to leftmost columns
result = rot90(result); % rotate back to original orientation

[JAI PRAKASH]

Wow, great help. Accurate logic.

Thanks a lot

Answer 2

[Image Analyst]

Use unique():

inputMatrix = [1 2 0;
  2 3 4;
  4 5 6]
[~, ia, ic] = unique(inputMatrix);
output = zeros(size(inputMatrix)); % Initialize
output(ia) = inputMatrix(ia)

[JAI PRAKASH]

Thanks for response. But it gives undesired results for some inputs.

e.g.

inputMatrix = [1 2 0;
         4 3 1;
         4 5 6]
output =

     1     2     0
     4     3     0
     0     5     6

outputShouldBe =
   2     0     0
   3     1     0
   4     5     6

[James Tursa]

So it appears you have added an additional requirement, that of moving elements to the left. Are there any other requirements that you haven't told us about?

[Walter Roberson]

That output contradicts the original pattern. For that "should be" output to be true, then the output for

input = [1 2 0;
         2 3 4;
         4 5 6];

should be

[1 2 0;
 3 4 0;
 5 6 0;]

[JAI PRAKASH]

@James Tursa

"Moving elements to the left" is not a mandatory requirement.

inputMatrix = [1 2 0;
         4 3 1;
         4 5 6]
outputCouldBe =
   0     2     0
   0     3     1
   4     5     6

Above output matrix also holds good :)

At the end, more priority given to bottom rows is what required.

I mean, the last row's elements are unchanged. 2nd last row's common elements turn to zero. 3rd last row's common elements(with 2nd last and very last rows) turn to zero.