Thank you everyone. After thinking about each response, I realized a fairly simple solution is available (obviously, other suggested approaches work as well):
stopifnot(length(x) == length(y); stopifnot(length(x) > 0) r <- list() for (i in 1:length(x) ) { r[[i]] <- cor(x = dat[, x[i] ], y = dat[, y[i] ]) } print(r) On Mon, Sep 10, 2018 at 11:30 AM Berry, Charles <ccbe...@ucsd.edu> wrote: > I have a sense of deja vu: > > https://www.mail-archive.com/r-help@r-project.org/msg250494.html > > There is some good advice there. > > > On Sep 9, 2018, at 3:49 PM, David Disabato <ddisa...@gmail.com> wrote: > > > > Hi R-help, > > > > I am trying to create a for loop with multiple iteration indexes. I don't > > want to use two different for loops nested together because I don't need > > the full matrix of the two indexes, just the diagonal elements (e.g., > i[1] > > & j[1] and i[2] & j[2], but not i[1] & j[2]). Is there a way to specify > > both i and j in a single for loop? Here is a simplified example of > > pseudo-code where x and y are equally sized character vectors with column > > names and dat is their dataframe (obviously this code doesn't run in R, > but > > hopefully you perceive my goal): > > > > r <- list() > > n <- 0 > > for (i in x; j in y) { > > n <- n + 1 > > r[[n]] <- cor(x = dat[, i], y = dat[, j]) > > } > > print(r) > > > > I realize there are other solutions to this particular correlation > example, > > but my actual problem is much more complicated, so I am hoping for a > > solution that generalizes across any code within the for loop. > > A more aRtful way (than a for loop) to approach this is with mapply: > > > i <- head(colnames(mtcars)) > j <- tail(colnames(mtcars)) > > r <- mapply(function(i, j, dat) cor( x = dat[, i], y = dat[, j]), > i=i , j=j , MoreArgs = list( dat = mtcars), > SIMPLIFY = FALSE, USE.NAMES = FALSE) > > > and if you want, maybe USE.NAMES = paste(i, j, sep="_") > > Chuck > > -- David J. Disabato, M.A. Clinical Psychology Doctoral Student George Mason University ddisa...@gmu.edu Email is not a secure form of communication as information and confidentiality cannot be guaranteed. Information provided in an email is not intended to be a professional service. In the case of a crisis or emergency situation, call 911. [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.