R help - Nov 2005 - Compiled name to object

Hi,

I have a tricky problem with composing a name that should represent an
object:

I want to pass a data frame and a string that contains a column name to
a function, e.g.:

    check(testFrame, "seconds")

The function should now divide the testFrame into two subsets and call a
t-test on the numbers that are in the given column:

    check <- function(frame, column) {
      sessionNo <- c("s01", "s02", "s03",
"s04", "s05", "s06")
      earlySessions <- subset(frame, frame$session %in% sessionNo)
      lateSessions <- subset(frame, !frame$session %in% sessionNo)
      t.test(earlySessions$column, lateSessions$column)
    }

How can I get R to change "earlySessions$column" to whatever was
passed
as string, in the above example "earlySessions$seconds"?

Thanks for any hint.
Claus

On Fri, 18 Nov 2005, Claus Atzenbeck wrote:
> How can I get R to change "earlySessions$column" to whatever was
passed
> as string, in the above example "earlySessions$seconds"?
In the meanwhile I received a solution: earlySessions[[column]]

Claus

Dear Claus

You can write

earlySessions[,"seconds"] instead of earlySessions$seconds and
with that syntax you can also use:

col1 <- "seconds"
earlySessions[,col1]

and you will get what you are looking for.

Best regards,

Christoph Buser

--------------------------------------------------------------
Christoph Buser <buser at stat.math.ethz.ch>
Seminar fuer Statistik, LEO C13
ETH (Federal Inst. Technology)	8092 Zurich	 SWITZERLAND
phone: x-41-44-632-4673		fax: 632-1228
http://stat.ethz.ch/~buser/
--------------------------------------------------------------


Claus Atzenbeck writes:
 > Hi,
 > 
 > I have a tricky problem with composing a name that should represent an
 > object:
 > 
 > I want to pass a data frame and a string that contains a column name to
 > a function, e.g.:
 > 
 >     check(testFrame, "seconds")
 > 
 > The function should now divide the testFrame into two subsets and call a
 > t-test on the numbers that are in the given column:
 > 
 >     check <- function(frame, column) {
 >       sessionNo <- c("s01", "s02", "s03",
"s04", "s05", "s06")
 >       earlySessions <- subset(frame, frame$session %in% sessionNo)
 >       lateSessions <- subset(frame, !frame$session %in% sessionNo)
 >       t.test(earlySessions$column, lateSessions$column)
 >     }
 > 
 > How can I get R to change "earlySessions$column" to whatever was
passed
 > as string, in the above example "earlySessions$seconds"?
 > 
 > Thanks for any hint.
 > Claus
 > 
 > ______________________________________________
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