Thanks Sarah. I have read about the problems with attach(), and I 
will try to avoid it.
I have now found the line that's causing the problem is:

>setwd("z:/homework")

With that line in place, either in a program or in Rprofile.site (?), 
then the moment I run R and simply enter (before reading any data)
summary(mydata)
I get sample statistics for a dozen variables!

Do not save the workspace? I thought the option to save/use a binary 
file is meant to be convenient.

I like working in the same working directory, and I like .rdata 
files. Does this sound hopeless? Thanks.

At 09:26 PM 11/15/2011, Sarah Goslee wrote:
>Hi,
>
>The obvious answer is don't use attach() and you'll never have
>that problem. And see further comments inline.
>
>On Tue, Nov 15, 2011 at 6:05 PM, Steven Yen <syen@utk.edu> wrote:
> > Can someone help me with this variable/data reading issue?
> > I read a csv file and transform/create an additional variable (called y).
> >
> > The first set of commands below produced different sample statistics
> > for hw11$y and y
> >
> > In the second set of command I renameuse the variable name yy, and
> > sample statistics for $hw11$yy and yy are identical.
> >
> > Using y <- yy fixed it, but I am not sure why I would need to do that.
> >
> > That "y" appeared to have come from a variable called "y" from
> > another data frame (unrelated to the current run).
> >
> > Help!
> >
> >  > setwd("z:/homework")
> >  > sink ("z:/homework/hw11.our", append=T, split=T)
> >  > hw11 <- read.csv("ij10b.csv",header=T)
> >  > hw11$y <- hw11$e3
> >  > attach(hw11)
> > The following object(s) are masked _by_ '.GlobalEnv':
> >     y
>
>Look there. R even *told* you that it was going to use the
>y in the global environment rather than the one you were
>trying to attach.
>
>The other solution: don't save your workspace. Your other
>email on this topic suggested to me that there is a .RData
>file in your preferred working directory that contains an
>object y, and that's what is interfering with what you think
>should happen.
>
>Deleting that file, or using a different directory, or removing
>y before you attach the data frame would all work.
>
>But truly, the best possible strategy is to avoid using attach()
>so you don't have to worry about which object named y is
>really being used because you specify it explicitly.
>
>
> >  > (n <- dim(hw11)[1])
> > [1] 13765
> >  > summary(hw11$y)
> >     Min.  1st Qu.   Median     Mean  3rd Qu.     Max.
> >   0.0000   0.4500   1.0000   1.6726   2.0000 140.0000
> >  > length(hw11$y)
> > [1] 13765
> >  > summary(y)
> >    Min. 1st Qu.  Median    Mean 3rd Qu.    Max.
> > 0.00000 0.00000 0.00000 0.24958 0.00000 1.00000
> >  > length(y)
> > [1] 601
> >  >
> >
> >  > setwd("z:/homework")
> >  > sink ("z:/homework/hw11.our", append=T, split=T)
> >  > hw11 <- read.csv("ij10b.csv",header=T)
> >  > hw11$yy <- hw11$e3
> >  > attach(hw11)
> >  > hw11$yy <- hw11$e3
> >  > summary(hw11$yy)
> >     Min.  1st Qu.   Median     Mean  3rd Qu.     Max.
> >   0.0000   0.4500   1.0000   1.6726   2.0000 140.0000
> >  > length(hw11$yy)
> > [1] 13765
> >  > summary(yy)
> >     Min.  1st Qu.   Median     Mean  3rd Qu.     Max.
> >   0.0000   0.4500   1.0000   1.6726   2.0000 140.0000
> >  > length(yy)
> > [1] 13765
> >  >
> >
>
>--
>Sarah Goslee
>http://www.functionaldiversity.org

--
Steven T. Yen, Professor of Agricultural Economics
The University of Tennessee
http://web.utk.edu/~syen/  
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