Hi David, Thank you so much for your kind suggestion and fixing my code!! I learn a lot from you today.
Ding -----Original Message----- From: David Winsemius [mailto:dwinsem...@comcast.net] Sent: Thursday, April 19, 2018 6:58 PM To: Ding, Yuan Chun <ycd...@coh.org> Cc: r-help@r-project.org Subject: Re: [R] create multiple categorical variables in a data frame using a loop [Attention: This email came from an external source. Do not open attachments or click on links from unknown senders or unexpected emails.] > On Apr 19, 2018, at 1:22 PM, David Winsemius <dwinsem...@comcast.net> wrote: > > >> On Apr 19, 2018, at 11:20 AM, Ding, Yuan Chun <ycd...@coh.org> wrote: >> >> Hi All, >> >> I want to create a categorical variable, cat.pfoa, in the file of pfas.pheno >> (a data frame) based on log2pfoa values. I can do it using the following >> code. >> >> pfas.pheno <-within(pfas.pheno, {cat.pfoa<-NA >> cat.pfoa[pfas.pheno$log2pfoa <=quantile(pfas.pheno$log2pfoa,0.25, >> na.rm =T)]<-0 cat.pfoa[pfas.pheno$log2pfoa >> >=quantile(pfas.pheno$log2pfoa,0.75, na.rm =T)]<-2 >> >cat.pfoa[pfas.pheno$log2pfoa >=quantile(pfas.pheno$log2pfoa,0.25, na.rm =T) >> &pfas.pheno$log2pfoa <=quantile(pfas.pheno$log2pfoa,0.75, >> na.rm =T)]<-1 } > > This would be somewhat more compact and easier to maintain if you used > findInterval (untested in the absence of a data object, which is your > responsibility): > > pfas.pheno <-within(pfas.pheno, { > cat.pfoa <- findInterval( log2pfoa , c(-Inf, quantile( > log2pfoa,c(.25,.75), Inf), na.rm =T), Inf)]-1 } ) > > > `findInterval` numbers its intervals from 1, so to get a sequence starting at > 0 just subtract 1. > > >> However, I have additional 7 similar variables, so I wrote the following >> code, but it does not work. >> >> for (i in c("log2pfoa","log2pfos", "log2pfna", "log2pfdea", "log2pfuda", >> "log2pfhxs", "log2et_pfosa_acoh", "log2me_pfosa_acoh")) { >> cat.var <- paste0("cat.",i) >> pfas.pheno <- within(pfas.pheno, {eval(parse(text= cat.var))<-NA > > Nope. Cannot use R like a macro processor, at least not easily. R names are > not the same as character vlaues. They "live in different realities". The > `get` and `assign` functions can be used to "promote" character values to > real R names and make assignments from and to what would otherwise be merely > character values. > > Perhaps this (also mostly untested (except for the strategy of making > `assign` creat a new dataframe column: > > for (i in c("log2pfoa","log2pfos", "log2pfna", "log2pfdea", "log2pfuda", > "log2pfhxs", "log2et_pfosa_acoh", > "log2me_pfosa_acoh")) { > cat.var <- paste0("cat.",i) > assign( cat.var, findInterval( get(i) , c(-Inf, quantile( get(i), > c(.25,.75), Inf), na.rm =T), Inf)]-1 } ), > envir=as.environment( get( pfas.pheno ) ) ) That wasn't good advice. I would rather suggest (but still untested in the absence of a good demo dataset from the OP): for (i in c("log2pfoa","log2pfos", "log2pfna", "log2pfdea", "log2pfuda", "log2pfhxs", "log2et_pfosa_acoh", "log2me_pfosa_acoh")) { cat.var <- paste0("cat.",i) pfas.pheno[[ cat.var ]] <- findInterval( get(i) , c(-Inf, quantile( get(i), c(.25,.75), Inf), na.rm =T), Inf)]-1 } The "[[<-" function supports character values as column names during assignment. > -- David Winsemius Alameda, CA, USA 'Any technology distinguishable from magic is insufficiently advanced.' -Gehm's Corollary to Clarke's Third Law --------------------------------------------------------------------- -SECURITY/CONFIDENTIALITY WARNING- This message (and any attachments) are intended solely f...{{dropped:28}} ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
