OBJ$"toto" works to... > b <- as.data.frame(matrix(1:4,2)) > b V1 V2 1 1 3 2 2 4 > b$"V1" [1] 1 2
but varname is not evaluated in OBJ$varname. ------------------------------------------------------------------- Jacques VESLOT CNRS UMR 8090 I.B.L (2ème étage) 1 rue du Professeur Calmette B.P. 245 59019 Lille Cedex Tel : 33 (0)3.20.87.10.44 Fax : 33 (0)3.20.87.10.31 http://www-good.ibl.fr ------------------------------------------------------------------- Joerg van den Hoff a écrit : > Stéphane Cruveiller wrote: > >>Dear R users, >> >>I have a simple question on variable manipulation. >>Imagine I have an object "OBJ" that has "toto" as one of its variables. >>I would like to understand why if I do >> >> > varname <- "toto" >> >> >OBJ$varname returns no results >> >>whereas >> >> > OBJ[varname] returns the column entitled >>"toto" >> >> >>Thanks for your help. >> >>Stéphane. >> > > > because if the value of `varname' is substituted in the expressions, in > the first case that yields > > OBJ$"toto" and in the second > OBJ["toto"] > > > the latter is valid, the former is not (you'd need `OBJ$toto' there), > read ` ?"$" ': > > "...Both '[[' and '$' select a single element of the list. The main > difference is that '$' does not allow computed indices, whereas > '[[' does. 'x$name' is equivalent to 'x[["name"]]'..." > > > not, too, the difference between `[' (sublist) and `[[' (single element > extraction) > > joerg > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
