Combine data sets a and b where the datasets have "gaps" or unique points.

Example:

Input

a = [1,0;
     2,1;
     3,5;
     5,2;
     6,3];

b = [1,2;
     3,6;
     4,3;
     6,4]

Output

d = [1,0,2;
     2,1,0;
     3,5,6;
     4,0,3;
     5,2,0;
     6,3,4];

Where d is the combination of a and b

Where there are gaps in a and b, there should be zeros in the resulting matrix.