You may want to read about several "apply" functions. They may help you do what you are trying.
-----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Fredrik Karlsson Sent: Saturday, June 11, 2011 3:13 AM To: R-Help List Subject: [R] How do I make proper use of the by() function? Dear list, I have a function that uses values from two vectors and spits out one new vector based on all the values of the two original vectors, and with the same length as them. Ok, I would now like to be able to apply that function simply on two columns in a data frame, divided by the levels of factors in the data frame. I'm trying to use by() for this, but the output is too hard to use. What I am doing is this: by(df, list(df$Factor1,df$Factor2),function(x) my_function(x$col1,x$col2),simplify=TRUE) and the output is too complex to be used in a simple way. Actually, I just want something like a data frame, where the results vectors are placed in one column and the conditions under which they were produced (i.e. the values of the factors according to which the data set were divided) in other columns. This does not seem to be provided by by(), and aggregate only provides me with the ability to use values from one column, right? So, are there other functions I could use? Thanks! /Fredrik -- "Life is like a trumpet - if you don't put anything into it, you don't get anything out of it." [[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.
