Hi Mark, study the following example. The two simulated dataframes are put in a list called listdata. The loop iterates throught the elements in the list and multiplies the last column "listdata[[i]][,length(listdata[[i]])]" by the column before the last "listdata[[i]][,length(listdata[[i]])-1]". This new columns is assigned to be the new column after the last of the respective dataframe in the list "listdata[[i]][,length(listdata[[i]])+1]"
x1=rnorm(100,0,1) x2=rnorm(100,0,1) x3=rnorm(100,0,1) x4=rnorm(100,0,1) data1=data.frame(x1,x2) data2=data.frame(x3,x4) listdata=list(data1,data2) for(i in 1:length(listdata)){ listdata[[i]][,length(listdata[[i]])+1]=listdata[[i]][,length(listdata[[i]]) ]*listdata[[i]][,length(listdata[[i]])-1] } HTH, Daniel ------------------------- cuncta stricte discussurus ------------------------- -----Ursprüngliche Nachricht----- Von: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] Im Auftrag von Mark Na Gesendet: Thursday, July 23, 2009 2:06 PM An: r-help@r-project.org Betreff: [R] How to perform a calculation in each element of my list? Hi R-helpers, I have a list containing 10 elements, each of which is a dataframe. I wish to add a new column to each list element (dataframe) containing the product of the last two columns of each dataframe. I'd appreciate any pointers, thanks! Mark Na [[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.