Printing Tuple!(...)[] using for loop?

[Kirill via Digitalmars-d-learn]

I have a `Tuple!(string, ..., string)[] data` that I would like 
to print out:
`a   b   c`
`1   2   3`
`4   5   6`

    Furthermore, I want to be able to print any N rows and M 
columns of that table. For instance:
        `b   c`
        `2   3`
        or
        `1   2   3`
        `4   5   6`
I am using for loops for that:

        // inside some function(rows, cols):
        immutable startFromRow = ...;
        immutable endWithRow = ...;
        immutable startFromCol = ...;
        immutable endWithCol = ...;
                        
        // print data
        for(size_t i = startFromRow; i < endWithRow; i++) {
                for(size_t j = startFromCol; j < endWithCol; j++) {
                        writef("%s", data[i][j]);
                }
                writef("\n");
        }

And the compiler puts out the following:
`Error: variable 'j' cannot be read at compile time`

I tried `data[i].expand[j]`, but the same error occurs anyway.

I have two questions:
1. How do I print the contents of a Tuple using for loops? Or any 
other method?
2. What am I missing? How does it actually work under the hood?

Thanks in advance. Any help is greatly appreciated.