Using the summarise function in package plyr is one way; taking df to be your data frame with variable names V1-V4,
library(plyr) summarise(subset(df, V3 == 'text3'), sum = sum(V4)) sum 1 134 Another is to use the data.table package: library(data.table) dt <- data.table(df) dt[V3 == 'text3', sum(V4)] [1] 134 A third route would be with package sqldf, something like sqldf(df, "select sum(V4) from df where V3 == 'text3'") but sqldf is messed up on my system (probably because I didn't install it properly) so the code is untested. HTH, Dennis On Thu, Mar 17, 2011 at 3:50 AM, e-letter <inp...@gmail.com> wrote: > On 15/03/2011, Francisco Gochez <fjgoc...@googlemail.com> wrote: > > Hi, > > > > What you are after is: > > > > datasubset <- dataset[ dataset[,3] == "text3", ] > > Thank you. For the set > > text1,23,text2,45 > text1,23,text3,78 > text1,23,text3,56 > text1,23,text2,45 > > Is it possible to write a function that selects rows containing > 'text3' and applies the function 'sum' to values '78' and '56'? The > control statements described in the document 'an introduction to r' > (Venables and Smith, 2010) suggest that the if statement would return > 'true', to prevent a sum function being applied to 'true' results. > > ______________________________________________ > 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. > [[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.
