Seems that the following makes what I want : attach(votesredac) tapply(value, list(name, content_id), mean)
Only thing is, I don't need to make a mean - there is only one or no value. VinceD wrote: > > Hello, > > First, thanks for your help (and sorry for my english !) > > I have a data frame in which each row represents a vote (in percent, only > 20,40, 60,80,100) of one person on one content, with three columns : name > (the name of the voters), content_id, vote : > > str(votesredac) > 'data.frame': 1000 obs. of 3 variables: > $ name : chr "Guillemette Faure" "Guillemette Faure" "Guillemette > Faure" "Pascal Rich\xe9" ... > $ content_id: num 385241 384926 384635 383266 384814 ... > $ value : num 100 100 100 20 100 100 20 100 100 100 ... > > I want to build a matrix with one column for each content and one line for > each user, containing the votes. This matrix can content NAs (each person > hasn't voted on all contents). If each row and column was labelled, would > be better. > > > Thanks again ! > -- View this message in context: http://www.nabble.com/build-matrix-with-the-content-of-one-column-of-a-data-frame-in-function-of-two-factors-tp18364752p18366233.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.