I guess you could iterate through the matrix, and check the neighbours for each cell, and copy the value of the neighbour if that is > 0 or set a new value if all the neighbours are 0. In pseudocode:
comp = 1
for i = 0 to n:
for j = 0 to n:
for nei : neighbours(i, j):
if nei > 0:
m[i,j] = nei
break
m[i,j] = comp
comp++
And neighbours are the 4 (or 2) adjacent neighbouring cells to (i, j)