[R] How to specify a variable name in the regression formula without hard coding it

[Bos, Roger]

I have a matrix called mat and y is the column number of my response and
x is a vector of the column numbers of my terms.  The variable name of y
can change, so I don't want to hardcode it.  I can find out the name as
follows:

>            names(mat)[y]
[1] "er12.l"

Then I can run the regression by hard coding the variable name as
follows:

>             mod <- try(rlm(er12.l ~ ., data=mat[zidx, c(y, x)]),
silent=TRUE)

But how would I do so without hard coding the name er12.l?

I set up a reproducible example.  In the following my regression formula
is aa ~ bb + cc, or more simply aa ~ .
How can I use the name of the first column without hard coding aa?

dat <- data.frame(aa=runif(50), bb=runif(50), cc=runif(50))
names(dat)[1]
lm(aa ~ ., data=dat[1:10,])

Thanks,

Roger
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