How to replace the trapped zeros by previous number in a given matrices keeping leading and trailing zeros fixed?

Hi Matlab experts,

I have a matrix

A=[ 0 0 0 1 0 2 3 1 2 3 0 0 0

1 2 2 1 1 2 3 1 2 3 1 3 4

0 1 0 1 0 0 0 1 2 1 1 2 2

2 1 2 1 0 0 0 0 1 1 1 1 1

1 0 0 1 1 1 1 1 2 2 2 1 1];

And I want to replace all trapped zeros by previous number. for instance, In first column we have 1 0 2 I want to change this into 1 1 2. Similarly, In third column, I want to replace 2 0 2 by 2 2 2. In fifth column 1 0 0 1 by 1 1 1 1. In sixth column, 2 0 0 1 by 2 2 2 1 and so on for all columns. Just want to replace by all trapped zeros in each column by its preceeding non-zero digit Keeping leading and trailing zeros fixed. So that my final matrix looks something like this...

A=[ 0 0 0 1 0 2 3 1 2 3 0 0 0

1 2 2 1 1 2 3 1 2 3 1 3 4

1 1 2 1 1 2 3 1 2 1 1 2 2

2 1 2 1 1 2 3 1 1 1 1 1 1

1 0 0 1 1 1 1 1 2 2 2 1 1];

[Voss]

What should the output be for A as follows?

A=[  0
     2
     1
     0
     0];

[Sushil Pokharel]

The lower matrix should be the output.

[Voss]

OK, let me rephrase. What if you have A as in your question, except A(4,2) is 0, like this:

A=[  0     0     0     1     0     2     3     1     2     3     0     0     0
     1     2     2     1     1     2     3     1     2     3     1     3     4
     0     1     0     1     0     0     0     1     2     1     1     2     2
     2     0     2     1     0     0     0     0     1     1     1     1     1
     1     0     0     1     1     1     1     1     2     2     2     1     1];
%          ^ I put a 0 in the 4th row (not a "trapped zero", I presume)

The method used in the Accepted Answer puts a 1 in that spot:

r=size(A,1);
c=size(A,2);
for i=2:r-1
    for j=1:c
        if A(i,j)==0
            A(i,j)=A(i-1,j);
        end
    end
end
disp(A)

     0     0     0     1     0     2     3     1     2     3     0     0     0
     1     2     2     1     1     2     3     1     2     3     1     3     4
     1     1     2     1     1     2     3     1     2     1     1     2     2
     2     1     2     1     1     2     3     1     1     1     1     1     1
     1     0     0     1     1     1     1     1     2     2     2     1     1

%          ^ 4th row, 2nd column is now 1

Is that the right thing to do?

[Sushil Pokharel]

hi there, I encountered this problem but I think it can be fixed in the following way...

Please let me know if you have any better idea to do it.

A=given;
B=A>0;
C=cummax(B,1);
C_das = cummax(B,1,'reverse');
% this will keep the leading and trailing zeros fixed.
D = C&C_das;
D=double(D);
D.*A_obtained % A_obtained is the matrix obtained from the arif's code.

Answer 1

[Arif Hoq]

try this:

A=[  0     0     0     1     0     2     3     1     2     3     0     0     0
     1     2     2     1     1     2     3     1     2     3     1     3     4
     0     1     0     1     0     0     0     1     2     1     1     2     2
     2     1     2     1     0     0     0     0     1     1     1     1     1
     1     0     0     1     1     1     1     1     2     2     2     1     1];
r=size(A,1);
c=size(A,2);
for i=2:r-1
    for j=1:c
        if A(i,j)==0
            A(i,j)=A(i-1,j);
        end
    end
end
disp(A)

     0     0     0     1     0     2     3     1     2     3     0     0     0
     1     2     2     1     1     2     3     1     2     3     1     3     4
     1     1     2     1     1     2     3     1     2     1     1     2     2
     2     1     2     1     1     2     3     1     1     1     1     1     1
     1     0     0     1     1     1     1     1     2     2     2     1     1

expected_output=[  0     0     0     1     0     2     3     1     2     3     0     0     0
     1     2     2     1     1     2     3     1     2     3     1     3     4
     1     1     2     1     1     2     3     1     2     1     1     2     2
     2     1     2     1     1     2     3     1     1     1     1     1     1
     1     0     0     1     1     1     1     1     2     2     2     1     1];
 isequal(A,expected_output)  % just for checking that input A and expected output is equal

ans = logical
   1

[Sushil Pokharel]

Dear Arif, Thank you so much for your immediate response. I really appreciate your help and for your time this is exactly what I needed.

[Arif Hoq]

my pleasure