Replace Specific Value in Specific part of the Main Matrix

Hello,

Suppose I have this Matrix

A=[0 1 2 2 2 0 1 0 2;0 1 1 1 1 1 1 1 0;2 1 2 1 1 2 1 2 0;0 0 1 0 1 1 1 0 2;0 2 0 1 0 2 0 1 2;0 0 1 2 2 2 2 0 2]

A =

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

I want to replace the value 1 to 0, only in one part of the matrix which is A(3:4,4:6), the other ones (1) and other values remain the same and unchanged. So The results I am expecting should be:

A =

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

How to do that?

I tried A(A(3:4,4:6)==1)=0, but It did Not give me the expected results, it gave me the following which changed the values of other elements, same thing happens when using find function.

A =

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

I also tried to divided the matrix into 9 parts, and change the part I want to be changed, then recombined these 9 parts (sub-matrices) to given the Main Matrix with required change, It worked! But is there a more efficient way to that,if yes I would be very glad, because dividing the matrix and recombine it, is kind of exhausting to do in my real problem.

Thanks in-advance Alaa

Answer 1

[Stephen23]

>> A = [0,1,2,2,2,0,1,0,2;0,1,1,1,1,1,1,1,0;2,1,2,1,1,2,1,2,0;0,0,1,0,1,1,1,0,2;0,2,0,1,0,2,0,1,2;0,0,1,2,2,2,2,0,2];
>> A(3:4,4:6) = A(3:4,4:6)-(A(3:4,4:6)==1)
A =
     0     1     2     2     2     0     1     0     2
     0     1     1     1     1     1     1     1     0
     2     1     2     0     0     2     1     2     0
     0     0     1     0     0     0     1     0     2
     0     2     0     1     0     2     0     1     2
     0     0     1     2     2     2     2     0     2

[Alaa Al-Saffar]

Thank you Stephen

Very simple and lovely solution. Now I can code my problem more smoothly.

Thank you again.

Answer 2

[Guillaume]

Another option is to save your matrix slice in a variable. Do whatever manipulation you need with that variable, then copy the modified slice back into the original matrix:

B = A(3:4, 4:6);
B(B == 1) = 0;
A(3:4, 4:6) = B;

[Alaa Al-Saffar]

Thank you Guillaume

This is also another simple and lovely solution.

Many thanks