[R] cannot turn some columns in a data frame into factors

[Sam Steingold]

> * 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?

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Sam Steingold (http://www.podval.org/~sds) on Fedora Core release 5 (Bordeaux)
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