[R] building a formula string bit by bit ..

[Esmail Bonakdarian]

Hello,

Still a newbie with R, though I have learned a lot from reading
this list. I'm hoping someone can help with this question:

I have two vectors, one for variables, and one for bits.

I want to build a string (really a formula) based on the values in my
vector of 1s and 0s in bits. If I have a one, I want to include the
corresponding entry in the vars vector, otherwise ignore it. Of course
the "bits" vector will not stay the same.

So for example:

   vars=c('X.1', 'X.2', 'X.3', 'X.4', 'X.5')

   bits=c(1, 0, 1, 1, 0)
   ones=which(bits==1)

should yield:

   "X.1 + X.3 + X.4"

where as

   bits=c(1, 1, 0, 0, 0)

would yield

   "X.1 + X.2"

the "which" operator gives me the index values, is there an easy and
*efficient* way to build this string so that I can pass it on to glm?
I can probably hack some ugly code together to do this, but it won't
be efficient, and it won't be elegant :-)

Can anyone help?

Thanks!