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 <slavr...@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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