Steve,

I tried to replicate your error, but couldn't do it.  The code below works 
just fine for me.  Does it for you?

# create an example data frame
Bridges <- data.frame(CONDITION=1:5, TRAFFIC=rnorm(5), WEATHER=rnorm(5))

# create new variable "LOG_COND"
Bridges$LOG_COND = log(Bridges$CONDITION, base = exp(1))

# fit linear model
lm.bridges = lm(LOG_COND ~ TRAFFIC + WEATHER, data = Bridges)

Jean


slavrenz <slavrenz@purdue.edu> wrote on 08/20/2012 02:30:31 PM:
> 
> Hello, I have question about referencing a variable that I created in a
> dataframe, and I am hoping the experts on here can be of assistance. I 
have
> a dataset of highway bridges with approximately 10,000 observations. I
> imported these into R in the form of a dataframe called "Bridges".
> 
> I am interested in running some basic linear models on a few key 
variables
> with the data. Say "CONDITION" is my dependent variable, and "TRAFFIC" 
and
> "WEATHER" are the independent variables I am considering. In order to
> capture a possible exponential relationship between "CONDITION", 
"TRAFFIC",
> and "WEATHER", I created the variable "LOG_COND":
> 
> Bridges$LOG_COND = log(Bridges$CONDITION, base = exp(1))
> 
> I then used the "str" command to verify that the variable shows up
> correctly, and is of the correct form (numeric) in the dataframe.
> 
> However, when I then attempt to use my new variable, say, for example:
> 
> lm.bridges = lm(LOG_COND ~ TRAFFIC + WEATHER, data = Bridges),      (not
> sure why the tilde symbol shows up as a minus sign here)
> 
> I get "Error in eval(expr, envir, enclos) : object 'LOG_COND' not found"
> 
> Can anyone enlighten me as to what I am doing wrong, and if possible, 
some
> basic code that I can use to rectify the situation? I am a pretty basic 
R
> user right now, so I'm definitely looking for something that is more
> functional than elegant.
> 
> Thanks,
> 
> -Steve

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