R help - Oct 2012 - Error in contrasts message when using logistic regression code.

I have a rather large data set (about 30 predictor variables)

I need to preform a logistic regression on this data. My response variable
is binary.

My code looks like this:

mylogit <- glm(Enrolled ~ A + B + C + ... + EE, data = data, family
binomial(link="logit"))

with A,B,C, ... as my predictor variables. Some categorical, some
continuous, some binary.

I run the code and get this error:

Error in `contrasts<-`(`*tmp*`, value = contr.funs[1 + isOF[nn]]) : 
  contrasts can be applied only to factors with 2 or more levels

Any ideas on how to fix this? I am fairly new to R so Im guessing there is
something missing/wrong in my logit code. 

Thanks!




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On Oct 23, 2012, at 1:43 PM, hoguejm <hoguejm at gmail.com> wrote:
> I have a rather large data set (about 30 predictor variables)
> 
> I need to preform a logistic regression on this data. My response variable
> is binary.
> 
> My code looks like this:
> 
> mylogit <- glm(Enrolled ~ A + B + C + ... + EE, data = data, family >
binomial(link="logit"))
> 
> with A,B,C, ... as my predictor variables. Some categorical, some
> continuous, some binary.
> 
> I run the code and get this error:
> 
> Error in `contrasts<-`(`*tmp*`, value = contr.funs[1 + isOF[nn]]) : 
>  contrasts can be applied only to factors with 2 or more levels
> 
> Any ideas on how to fix this? I am fairly new to R so Im guessing there is
> something missing/wrong in my logit code. 
> 
> Thanks!

More than likely, one or more of your categorical variables are not set up as
factors, or if they are, then one or more have only a single factor level
present in the dataset that is used for the model, thus are constant.

You might want to run:

  # see ?str
  str(data)

and:

  # see ?summary
  summary(data)

to get a sense of the structure of your data set (to make sure that you have
factors and not character vectors) and to get a sense for the distribution of
your IVs.

Regards,

Marc Schwartz

How to change categorical vars to factors. 
I am very new at R

Thanks



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On Oct 23, 2012, at 1:57 PM, hoguejm wrote:
> How to change categorical vars to factors. 
There is nio such thing as a "categorical var" in R, although the
closest thing to one is a factor class vector. If you have either numeric or
character vectors and you want them to become factors:

facvar <- factor(oldvar)

> I am very new at R
Yes. Consider abandoning Nabble. And do read the Posting Guide.

> View this message in context:
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> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> R-help at r-project.org mailing list
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
Alameda, CA, USA