Actually it does -- one has to use feed the result back into the original variable:
add.col <- function(df, vec, namevec){ if (nrow(df) < length(vec) ){ df <- # pads rows if needed rbind(df, matrix(NA, length(vec)-nrow(df), ncol(df), dimnames=list( NULL, names(df) ) ) ) } length(vec) <- nrow(df) # pads with NA's df[, namevec] <- vec; # names new col properly return(df) } mydata <- NULL mydata <- data.frame(userid = c(5, 6, 5, 6, 5, 6), taskid = c(1, 1, 2, 2, 3, 3), stuff = 11:16) mydata <- add.col(mydata, c(1,2,3,4),"test1") mydata <- add.col(mydata, c(1,2,3,4,5,6,7,8),"test2") mydata Thanks a lot, David and all others here you made the effort! Ralf On Tue, Aug 3, 2010 at 10:37 PM, David Winsemius <dwinsem...@comcast.net> wrote: > > On Aug 3, 2010, at 10:35 PM, David Winsemius wrote: > >> >> On Aug 3, 2010, at 8:32 PM, Ralf B wrote: >> >>> Hi experts, >>> >>> I am trying to write a very flexible method that allows me to add a >>> new column to an existing data frame. This is what I have so far: >>> >>> add.column <- function(df, new.col, name) { >>> n.row <- dim(df)[1] >>> length(new.col) <- n.row >>> names(new.col) <- name >>> return(cbind(df, new.col)) >>> } >>> >>> df <- NULL >>> df <- data.frame(a=c(1,2,3)) >>> df >>> # corect: added NA to new collumn >>> df <- add.column(df,c(1,2),'myNewColumn2') >>> df >>> # problem: not added, data frame should be extended with NAs >>> add.column(df,c(1,2,3,4),'myNewColumn3') >>> df >>> >>> >>> However, there are two problems: >>> >>> 1) The column name is not renamed accurately but always set to >>> 'new.col' . Surely this could be done outside the function, but it >>> would be better if its self contained. >> >> Try this: >> >> add.col <- function(df, vec, namevec){ >> length(vec) <- nrow(df) # pads with NA's >> cbind(df, namevec=vec)} # names new col properly >> > Actually it doesn't name column correctky... see below for a method with "[ > <-" . > >>> 2) It does not work for cases where new.col is longer than the length >>> of the data frame. In such cases, I would like to add NA's to the data >>> frame if it has less rows. >> >> Don't have a compact answer to this. (Tried re-dimensioning with "dim() >> <-" but it was not accepted by the interpreter. Would need to add a test >> at the beginning and then pad with rows of NA's using rbind before cbinding >> as above. >> >> add.col <- function(df, vec, namevec){ >> if (nrow(df) < length(vec) ){ df <- # pads rows if needed >> rbind(df, matrix(NA, length(vec)-nrow(df), ncol(df), >> dimnames=list( NULL, names(df) ) ) ) } >> length(vec) <- nrow(df) # pads with NA's >> df[, namevec] <- vec; # names new col properly >> return(df)} >> >>> >>> Any ideas to to solve this? >> >> Has not been tested with columns of varying types. >> > > David Winsemius, MD > West Hartford, CT > > ______________________________________________ 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.