with(dftest,aggregate(cbind(x,y),list(z),FUN=mean)) # Group.1 x y #1 0 7 1 #2 1 6 2
#or library(plyr) ddply(dftest,.(z),numcolwise(mean)) # z x y #1 0 7 1 #2 1 6 2 A.K. ----- Original Message ----- From: jpm miao <miao...@gmail.com> To: r-help <r-help@r-project.org> Cc: Sent: Thursday, May 23, 2013 3:05 AM Subject: [R] convert a character string to a name Hi, From time to time I need to do the aggregation. To illustrate, I present a toy example as below. In this example, the task is to aggregate x and y by z with the function mean. Could I call the aggregation function with x_test, where x_test=c("x","y")? Thanks Miao > dftest<-data.frame(x=1:12, y=(1:12)%%4, z=(1:12)%%2) > dftest x y z 1 1 1 1 2 2 2 0 3 3 3 1 4 4 0 0 5 5 1 1 6 6 2 0 7 7 3 1 8 8 0 0 9 9 1 1 10 10 2 0 11 11 3 1 12 12 0 0 > aggregate(cbind(x,y)~z, data=dftest, FUN=mean) z x y 1 0 7 1 2 1 6 2 > x_test=c("x","y") > aggregate(cbind(x_test)~z, data=dftest, FUN=mean) Error in model.frame.default(formula = cbind(x_test) ~ z, data = dftest) : variable lengths differ (found for 'z') a1aggregate(cbind(factor(x_test))~z, data=dftest, FUN=mean) Error in model.frame.default(formula = cbind(factor(x_test)) ~ z, data = dftest) : variable lengths differ (found for 'z') > aggregate(factor(x_test)~z, data=dftest, FUN=mean) Error in model.frame.default(formula = factor(x_test) ~ z, data = dftest) : variable lengths differ (found for 'z') [[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.