The culprit is the cbind function. When given 2 vectors (not already something else), cbind will create a matrix, not a data frame. A matrix can only have 1 type, so the numbers get converted to character. In your first example you never do create a data frame, you just build a matrix (try str(results)) so fix cannot change a single column to numeric in something that is a matrix. In the second example you do create a data frame so fix will allow changing of columns, but the cbind inside the call to data.frame is still creating a matrix (and converting numeric to character) before it is included in the data frame. Remove the cbind and just do:
out1 <- data.frame(species=as.character(paste(s)),obsnum=obsnum) and then out1 will be a data frame without ever converting the number obsnum to a character. Hope this helps, -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- > project.org] On Behalf Of Alan Smith > Sent: Wednesday, February 18, 2009 2:01 PM > To: r-help@r-project.org > Subject: [R] understanding how R determines numbers and characters when > creating a data frame > > Hello R Users and Developers, > > I have a basic question about how R works. Over the past few years I > have > struggled when I try to generate a new data frame that I believe should > contain numeric data in some columns and character data in others only > to > find everything converted to character data. Is there a general method > to > create data frames that contain the data in the desired format: > numbers as > numeric and character as a factor etc? I often have this problem and > in the > worst case I have to export the file and read it back it in. I have > emulated a simple example of the problem. It often happens while using > "for" loops. Could someone explain how to avoid this problem by > properly > creating data frames in for loops that can contain both numeric and > character data. > > > > ********Question for example 1. > > Why does the cbind command convert the numeric data to character data? > Why > can't the character data be converted to numeric data using the fix > command? > > > ### Example 1 ############# > > data(iris) > > obsnum<-NULL > > results<-NULL > > for(s in unique(as.character(iris$Species))){ > > temp1<-iris[iris$Species==s,] > > obsnum<-length(unique(temp1$Sepal.Length)) # a number > > out1<-cbind(species=as.character(paste(s)),obsnum) # number converted > to > character > > results<-rbind(out1,results) > > } > > results > > #fix(results) # cannot convert obsnum to numeric using fix > > #################################### > > > > ******Question for example 2 > > Why does adding the data.frame command allow the character data to be > converted to numeric data using fix command? > > ### Example 2 ############# > > data(iris) > > obsnum<-NULL > > results<-NULL > > for(s in unique(as.character(iris$Species))){ > > temp1<-iris[iris$Species==s,] > > obsnum<-length(unique(temp1$Sepal.Length)) > > out1<-data.frame(cbind(species=as.character(paste(s)),obsnum)) # number > converted to character > > results<-rbind(out1,results) > > } > > results > > #fix(results) # can now convert obsnum to numeric using fix > > > > ###### > > > > > > Thank you, > > Alan Smith > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list > 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. ______________________________________________ R-help@r-project.org mailing list 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.
