Hi Rob, Here is one approach:
## define a function that does the calculations ## (the covariance of two vectors divided by the square root of ## the products of their variances is just a correlation) rF <- function(x, a, b) cor(x[a], x[b], use = "complete.obs") set.seed(1) bigdata <- matrix(rnorm(271 * 13890), ncol = 271) results <- apply(bigdata, 1, FUN = rF, a = 174:213, b = 214:253) ## combine bigdata <- cbind(bigdata, iecorr = results) Hope this helps, Josh On Tue, Nov 15, 2011 at 8:42 AM, robgriffin247 <robgriffin...@hotmail.com> wrote: > Just as an update on this problem: > I have managed to get the variance for the selected columns > > Now all I need is the covariance between these 2 selections - > the two target columns are and the aim is that a new column contain a > covariance value between these on each row: > > maindata[,c(174:213)] and maindata[,c(214:253] > > I've played around with all sorts of apply (and derivatives of apply) and in > various different setups so I think I'm close but I feel like I'm chasing my > tail here! > > -- > View this message in context: > http://r.789695.n4.nabble.com/correlations-between-columns-for-each-row-tp4039193p4073208.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > 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. > -- Joshua Wiley Ph.D. Student, Health Psychology Programmer Analyst II, ATS Statistical Consulting Group University of California, Los Angeles https://joshuawiley.com/ ______________________________________________ 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.
