[R] the difference between "x1" and x1

[Gabor Grothendieck]

Try this:

# test data
set.seed(1)
DF <- data.frame(x1 = rnorm(5), x2 = rnorm(5), x3 = rnorm(5))
DF
model.list <- c("x2", "x3")

# transform
for(v in model.list) DF[v] <- floor(DF[v])

On 4/20/06, Chad Reyhan Bhatti <bhatticr at stat.rice.edu> wrote:
> Hello,
>
> I am not sure what to write in the subject line, but I would like to take
> a character string that is a variable in a data frame and apply a function
> that takes a numeric argument to this character string.
>
> Here is a simplified example that would solve my problem.
> Imagine I have my data stored in a data frame.
> > x1 <- x2 <- x3 <- x4 <- x5 <- rnorm(20,0,1);
> > data <- as.data.frame(cbind(x1,x2,x3,x4,x5));
>
> I have a vector containing the variables of interest as such.
> > model.list <- c("x1","x3","x4");
>
> > model.list[1]
> [1] "x1"
>
> I would like to loop through this vector and apply the floor() function to
> each variable.  In the current form the elements of model.list do not
> represent the variables in the data frame.
>
> > floor(model.list[1])
> Error in floor(model.list[1]) : Non-numeric argument to mathematical
> function
>
> > floor(eval(model.list[1]))
> Error in floor(eval(model.list[1])) : Non-numeric argument to mathematical
> function
>
> > s <- expression(paste("floor(",model.list[1],")",sep=""))
> > s
> expression(paste("floor(", model.list[1], ")", sep = ""))
> > eval(s)
> [1] "floor(x1)"
> >
>
> I have tried the obvious (to me) without success.  Perhaps someone could
> suggest a
> solution and some tidbits for me to read up on about the how and why.
>
> Thanks,
>
> Chad R. Bhatti
>
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