Make a better code to check the neighbours of a cell in a matrix and replace a value

Hello, I want to ask for help to make my code better, or maybe simpler. My idea is to check the 8 neighbors of my cell isla(i,j)==2 and if one of them has the value 0, insert in that location the value 2, but only in the first one that the code finds.

My code is:

for i=3:len+2
    for j=3:len+2
        if isla(i,j)==2 
            if isla(i,j+1)==0 %espacio a la derecha vacio
                isla(i,j+1)=2;
            elseif isla(i,j-1)==0 %espacio a la izquierda vacio
                 isla(i,j-1)=2;
            elseif isla(i+1,j)==0 %espacio de abajo vacio
                 isla(i+1,j)=2;
            elseif isla(i-1,j)==0 %espacio de arriba vacio
                 isla(i-1,j)=2;
            elseif isla(i-1,j-1)==0
                isla(i-1,j-1)=2;
            elseif isla(i-1,j+1)==0
                isla(i-1,j+1)=2;
            elseif isla(i+1,j+1)==0
                isla(i+1,j+1)=2;
            elseif isla(i+1,j-1)==0
                isla(i+1,j-1)=2;
            end
end 
end
end
end

Hope you can see the problem is that the code isn't simple. I wish I could use fewer lines to don't have to modify the entire code every time when I have to change the conditions. I hope someone can help me. I apologize if I misspelled a word, English isn't my native language. Greetings

Answer 1

[Image Analyst]

Do you have the Image Processing Toolbox? And are all the numbers guaranteed to be 0 or positive?

If you want any neighbor of a 2 that is a 0 to be set to 2, then don't use elseif - have separate if statements.

if isla(i,j+1)==0 %espacio a la derecha vacio
                isla(i,j+1)=2;
end
if isla(i,j-1)==0 %espacio a la izquierda vacio
                 isla(i,j-1)=2;
end
if isla(i+1,j)==0 %espacio de abajo vacio
                 isla(i+1,j)=2;
end
if isla(i-1,j)==0 %espacio de arriba vacio
                 isla(i-1,j)=2;
end
if isla(i-1,j-1)==0
                isla(i-1,j-1)=2;
end
if isla(i-1,j+1)==0
                isla(i-1,j+1)=2;
end
if isla(i+1,j+1)==0
                isla(i+1,j+1)=2;
end
if isla(i+1,j-1)==0
                isla(i+1,j-1)=2;
end

[ferne17]

Actually I don't want that every neighbour be 2, just the first one that the code can find in an arbitrarian order that I give to search, I'm looking for a more simple code, but aparently they all use Toolbox and do more complex things that what I want.

[Image Analyst]

Then put the order of the "if"s in the order that you want, and inside each one put "continue" so that once it gets inside the first "if" it will go to the bottom of the loop and skip all the other ifs. For example:

if isla(i-1,j-1)==0
   isla(i-1,j-1)=2;
   continue;
end

Do that in all the ifs.

Answer 2

[Ahmet Cecen]

If I understand correctly from your comment at the previous answer here is a pseudo-code that can do this in a somewhat simpler manner:

ok=0

While ok=0

i= a random number within the bounds of your index (use matlab help to find the function rand)

j= another random number

if isla(i,j)==0 && ( isla(i+1,j)==2 isla(i-1,j)==2 isla(i,j+1)==2 isla(i,j-1)==2 ) %Put as many neighbors within the OR logic as you want.

isla(i,j)=2;

ok=1;

endif

end

[Ahmet Cecen]

Hmm the ORs didnt show up on the text.

It is supposed to be:

if isla(i,j)==0 AND ( isla(i+1,j)==2 OR isla(i-1,j)==2 OR isla(i,j+1)==2 OR isla(i,j-1)==2 )