Filling up gaps in matrix's rows - matlab

Question

Let g be a matrix containing ones\zeroes. I want to fill up gaps of zeros (complete ones sequences) in the rows of g which are smaller then a given k.
For example fill up with ones all gaps smaller then three zeros. This code will work:
[m,n]=size(g);
k=3
for i=1:m
j=1
while (j<n)
if(g(i,j)==0)
flag=0;
for w=1:k
if(g(i,j+w-1)==1)
flag=1;
end
end
if(flag)
for w=1:k
g(i,j+w-1)=1;
end
else
while(~flag&j<n)
j=j+1;
if(g(i,j)==1)
flag=1;
end
end
end
end
j=j+1;
end
end
Is there a way to do so without all the for loops?

Answer 1

A short version using some built-in function:
M = [1 1 1 1 1
1 1 1 0 0
1 1 1 0 1
1 1 0 0 0
0 1 1 1 1]
Mopen = ~imopen(~padarray(M,[0,1],1),strel('line',3,0));
Mfill = Mopen(:,2:end-1);

Answer 2

A vectorized version:
k = 3;
d = diff( g,1,2);
L = d ~= 0;
c = cumsum([zeros(size(g,1),1) L],2)+1;
b = bsxfun(#plus, c, cumsum([0; c(1:end-1,end)]));
a =accumarray(reshape(b.',[],1),1);
f= find(a<k);
g(ismember(b,f) & g==0) = 1;
Example :
g =
1 1 1 1 1
1 1 1 0 0
1 1 1 0 1
1 1 0 0 0
0 1 1 1 1
result =
1 1 1 1 1
1 1 1 1 1
1 1 1 1 1
1 1 0 0 0
1 1 1 1 1

Answer 3

Another potential solution is to cast each row to a char array and then perform substitutions based on a regular expressions
g = round(rand(30,70));
figure();
subplot(121);
imagesc(g)
[m,n]=size(g);
k=3;
pattern = ['(?<!',char(0),')(',char(0),'{1,',num2str(k-1),'})(?!',char(0),')'];
for i=1:m
[matchstart,matchend] = regexp(char(g(i,:)),pattern);
for j = 1:length(matchstart)
g(i,matchstart(j):matchend(j)) = 1;
end
end
subplot(122);
imagesc(g)