This seems to have worked for me:


> df <- data.frame(a=1:10, b=1:10, c=1:10)
> str(df)
`data.frame':   10 obs. of  3 variables:
 $ a: int  1 2 3 4 5 6 7 8 9 10
 $ b: int  1 2 3 4 5 6 7 8 9 10
 $ c: int  1 2 3 4 5 6 7 8 9 10
> df.names <- attr(df,"names")
> factors <- 'c'
> sapply(factors, function (name) {
+    pos <- match(name,df.names)
+    if (is.na(pos)) stop(paste(name,": no such column\n"))
+    df[[pos]] <<- factor(df[[pos]])
+    cat(name,"(",pos,"):",is.factor(df[[pos]]),"\n")
+ })
c ( 3 ): TRUE
$c
NULL

> cat("factors:",sapply(df,is.factor),"\n")
factors: FALSE FALSE TRUE
> str(df)
`data.frame':   10 obs. of  3 variables:
 $ a: int  1 2 3 4 5 6 7 8 9 10
 $ b: int  1 2 3 4 5 6 7 8 9 10
 $ c: Factor w/ 10 levels "1","2","3","4",..: 1 2 3 4 5 6 7 8 9 10
>





On 5/11/06, Sam Steingold <sds@podval.org> wrote:
>
> > * jim holtman <wubygzna@tznvy.pbz> [2006-05-11 12:27:39 -0400]:
> >
> > try '<<-' as the assignment to make it global.
> >
> >      df[[pos]] <<- factor(df[[pos]])
>
> nothing changed -- I observe the exact same behaviour:
>
> Month ( 1 ): TRUE
> factors: FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
>
>
> > On 5/11/06, Sam Steingold <sds@podval.org> wrote:
> >>
> >> Hi,
> >> I have a data frame df and a list of names of columns that I want to
> >> turn into factors:
> >>
> >> df.names <- attr(df,"names")
> >> sapply(factors, function (name) {
> >>    pos <- match(name,df.names)
> >>    if (is.na(pos)) stop(paste(name,": no such column\n"))
> >>    df[[pos]] <- factor(df[[pos]])
> >>    cat(name,"(",pos,"):",is.factor(df[[pos]]),"\n")
> >> })
> >> cat("factors:",sapply(df,is.factor),"\n")
> >>
> >> the output is:
> >>
> >>
> >> Month ( 1 ): TRUE
> >> factors: FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
> >>
> >>
> >> i.e., there is a column named "Month" (the 1st column), and it is
> indeed
> >> turned into a factor inside sapply(), but after that it is numerical
> >> again!
> >>
> >> what am I doing wrong?
>
> --
> Sam Steingold (http://www.podval.org/~sds) on Fedora Core release 5
> (Bordeaux)
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-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390 (Cell)
+1 513 247 0281 (Home)

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