Dear Alex, > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of Alex Zhang > Sent: December-27-11 2:14 PM > To: r-help@r-project.org > Subject: [R] sapply Call Returning " the condition has length > 1" > Error > > Dear all, > > Happy new year! > > I have a question re using sapply. Below is a dummy example that would > replicate the error I saw. > > ##Code Starts here > DummyFunc <- function(x) { > > if (x > 0) { > return (x) > } else > { > return (-x) > } > > } > > Y = data.frame(val = c(-3:7)) > sapply(Y, FUN = DummyFunc) > ##Code ends here > > When I run it, I got: > val > [1,] 3 > [2,] 2 > [3,] 1 > [4,] 0 > [5,] -1 > [6,] -2 > [7,] -3 > [8,] -4 > [9,] -5 > [10,] -6 > [11,] -7 > Warning message: > In if (x > 0) { : > the condition has length > 1 and only the first element will be used > > The result is different from what I would expect plus there is such an > error message.
This is a warning, not really an error message. A data frame is essentially a list of variables (columns), and sapply() applies its FUN argument to each list element, that is, each variable -- the one variable val in your case. That produces a warning because val > 0 is a vector of 11 elements, and the first comparison, 3 > 0, which is TRUE, controls the result. > > I guess if the DummyFunc I provided is compatible with vectors, the > problem would go away. But let's suppose I cannot change DummyFunc. Is > there still a way to use sapply or alike without actually writing a > loop? Thanks. Well, you could just use > abs(Y$val) [1] 3 2 1 0 1 2 3 4 5 6 7 but I suppose that you didn't really want to write your own version of the absolute-value function as something more than an exercise. An alternative is > with(Y, ifelse(val > 0, val, -val)) [1] 3 2 1 0 1 2 3 4 5 6 7 I hope this helps, John -------------------------------- John Fox Senator William McMaster Professor of Social Statistics Department of Sociology McMaster University Hamilton, Ontario, Canada http://socserv.mcmaster.ca/jfox > > - Alex > [[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.
