I keep coming back to this problem of singular fits in rlm (MASS library),
but cannot figure out a good solution.

I am fitting a linear model with a factor variable, like
lm( Y ~ factorVar)
and this works fine. lm knows to construct the contrast matrix the way I
would expect, which puts the first factor as the baseline level.

But when I try
rlm( Y ~ factorVar)
I get the message "'x' is singular: singular fits are not implemented in
rlm."

How can I solve this problem so that I can use factor variables in rlm?

I've tried constructing the contrast matrix myself using the various "contr"
functions, but I always run out of memory. So I must not be doing something
right, because lm has to create some version of the same contrast matrix in
memory. In any case, I don't think that more memory is the solution.

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