[R] creating a variable using concatenation

[zubin]

A general problem i run into, i know there must be a simple solution. 

I like to create a variable by appending a 1 for example, (i need to
loop later on from 1 to X, thus the reason for this).   So i assign the
variable vplot with this value, however it has quotes and when i use it
in a barplot, it throws an error.  but the tcenter$X1 does exist, its an
element of a data frame.  So if i type directly it works, but i like to
do this programmatically, as i have to generate a bunch of these plots
and need to loop. 

So how do i concatenate to create a variable, then reference that
variable in a function call?


R> x <- data.frame(1,2,3,4,5,6,7,8)
R> x
  X1 X2 X3 X4 X5 X6 X7 X8
1  1  2  3  4  5  6  7  8
R> x$X1
[1] 1

R> i=1
R> toplot <- paste("x$X",i,sep="")
R> toplot
[1] "x$X1"

okay lets test:

 R> plot(x$X1)
-it works i see the plot

however this DOES not work

R> plot(toplot)

Error in plot.window(...) : need finite 'ylim' values
In addition: Warning messages:
1: In xy.coords(x, y, xlabel, ylabel, log) : NAs introduced by coercion
2: In min(x) : no non-missing arguments to min; returning Inf
3: In max(x) : no non-missing arguments to max; returning -Inf


Thus, that's my problem, i know it must be simple -  the variable is equal to x$X1 but it does not work in a function call?  i tried many functions - always some type of error.