[R] Handle lot of variables - Regression

anna0102 kleines911 at hotmail.com
Wed Oct 14 13:06:27 CEST 2009


Hey,

I've got a data set (e.g. named Data) which contains a lot of variables, for
example: s1, s2, ..., s50

My first question is:
It is possible to do this: Data$s1
But is it also possible to do something like this: Data$s1:s50 (I've tried a
lot of versions of those without a result)

My second question:
I want to do a stepwise logistic regression. For this purpose I use the
following procedures:
result<-glm(...)
step(result, direction="forward)

Now the problem I have, is, that I have to include all my 50 variables
(s1-s50), but I don't want to write them all down like y~s1+s2+s3+s4...
(furthermore it has to be implemented in a loop, so I really need it).
I've tried do store the 50 variables in a list (e.g. list[[1]]) and tried
this:
result<-glm(y ~ list[[1]], ...)
This works! But if I try to do it stepwise
result2<-step(result)
I always get the same results as from glm without a stepwise approach. So
obviously R can't handle this if you put a list in.
How can I make this work?

Thanks in advance,
Anna

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