combining string values

[Jason Stover]

I'm still working on incorporating interactions into
the computation of the covarinace matrix.

I need to combine multiple string values into a single
string, in a one-to-one way. For example, in the following
data set, there are two variables, each with two values:

        var1            var2
        ae              f
        a               ef

I don't want to just concatenate the values because
I would have aef in both cases.

I can work around this by using strtol, or something
like it. Two questions:

1. Is there some other function I should use?

2. Will this approach cause problems in the future if the union value
contains a long string?

-Jason