VS 2008 - Merge Two Text Files (Rows And Columns)

I have two text files. The first text file has the format:
ID h1 h2 h3
a 1 5 7
b 3 3 5
c 0 4 8

And the second file:
ID h4 h5 h6
a 2 4 9
b 3 6 1
b 4 1 5

Now I want to merge two files. The output likes
ID h1 h2 h3 h4 h5 h6
a 1 5 7 2 4 9
b 3 3 5 3 6 1
b 4 1 5
c 0 4 8

The two files has the same rows and columns. For the first rows(except header) in the two files, they have the same first column. Therefore just a simple append. The final first row becomes
a 1 5 7 2 4 9
The question is in the first only has one
b
and the second file has two

I want the maximum count of items from each list in the resultant list. I put some white spaces after "b" then append strings.
b 4 1 5
For key "c", because it is only in the first file and not in the second file, so I append white spaces after the corresponding strings.