On Dec 2, 2012, at 12:46 PM, Audrey wrote:
I am trying to write a function to change the case of all of the
text in a
data frame to lower case.
Define what you mean by "text".
I do not have foreknowledge of the data frame
names or the data types of each column.
It seems that if one references the data frame by index, then it
returns
class "data.frame" but if it is referenced by name, it returns class
"factor" or whatever the column actually is:
dat[1] returns class "data.frame" but
dat$name returns class "factor"
Yes. That is correct.
The problem is that, when one applies the tolower() and toupper()
functions,
dat$name will return a column of lower/uppercase returns (now class
"character") but dat[1] will return an array of factor level indexes.
It return an integer vector with attributes: class = factor and levels.
Specifying dat[1] as.character during the function call does not
work (e.g.
tolower(as.character(dat[1]))).
Because dat[1] is a list, not a vector.
So, I would loop over the column names, but I can not figure out how
to
generically call them:
tst=names(dat);
dat$(tst[1]) returns an error
dat[tst[1]] returns class data.frame again
Thank you in advance!
change_case<-function(dat,wcase){
# change case
res=sapply(dat,class); # get classes
ind<-res=='character';
dat[ind]<-switch(wcase,
'lower'=tolower(dat[ind]),
'upper'=toupper(dat[ind])
)
rm(ind);
ind<-res=='factor';
dat[ind]<-switch(wcase,
'lower'=factor(tolower(as.character(dat[ind]))),
'upper'=factor(toupper(as.character(dat[ind])))
)
return(dat);
}
You probably need to study the help("[") page and learn the difference
between "[" and "[[". Changing to "[[" in a couple of places would
probably allow success.
--
David Winsemius, MD
Alameda, CA, USA
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