R help - May 2006 - cannot turn some columns in a data frame into factors

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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try '<<-' as the assignment to make it global.

     df[[pos]] <<- factor(df[[pos]])



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)
> http://honestreporting.com http://truepeace.org
> http://openvotingconsortium.org
> http://thereligionofpeace.com http://memri.org http://palestinefacts.org
> UNIX, car: hard to learn/easy to use; Windows, bike: hard to learn/hard to
> use.
>
> ______________________________________________
> R-help@stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
> http://www.R-project.org/posting-guide.html
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390 (Cell)
+1 513 247 0281 (Home)

What is the problem you are trying to solve?

	[[alternative HTML version deleted]]

> * jim holtman <wubygzna at 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 at 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)
http://pmw.org.il http://ffii.org http://memri.org http://palestinefacts.org
http://truepeace.org http://mideasttruth.com http://dhimmi.com
If you're being passed on the right, you're in the wrong lane.

Thanks to everyone who took time to respond, both here on the list and
via private e-mail (I do read the list on gmane, so there is not reason
to CC me).

it turned out that R passes _structured_ arguments by value.

the solution I use now is:

  df[factors] = lapply(df[factors],factor)

  if (!all(sort(names(df)[sapply(df,is.factor)]) == sort(factors)))
    stop(paste("bad
factors:",sort(names(df)[sapply(df,is.factor)]),"!=",
               sort(factors)))

it is based on a private e-mail reply by Phil Spector.
> * Sam Steingold <fqf at cbqiny.bet> [2006-05-11 12:09:26 -0400]:
>
> 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)
http://camera.org http://iris.org.il http://dhimmi.com
http://memri.org http://ffii.org http://jihadwatch.org http://pmw.org.il
PI seconds is a nanocentury