?var points out that "var is another interface to cov", i.e. it calculates (possibly part of) the "variance" matrix. In the simplest special case y = x and you get the entire variance matrix, or just the sample variance if x is a simple vector, as in your case.
BTW you little function is a bit more complicated than it need be, isn't it? > my.var <- function(x) sum((x-mean(x))^2)/(length(x)-1) would do the same job with many fewer parentheses.... Bill Venables CSIRO Laboratories PO Box 120, Cleveland, 4163 AUSTRALIA Office Phone (email preferred): +61 7 3826 7251 Fax (if absolutely necessary): +61 7 3826 7304 Mobile: +61 4 8819 4402 Home Phone: +61 7 3286 7700 mailto:[EMAIL PROTECTED] http://www.cmis.csiro.au/bill.venables/ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ista Zahn Sent: Thursday, 25 October 2007 11:35 AM To: r-help@r-project.org Subject: [R] Novice programing question Hi all, I apologize for the ignorance implicit in this question, but I'm having a hard time figuring out how R functions work. For example, if I wanted to write a function to compute a variance, I would do something like >my.var <- function(x) (sum(((x-mean(x)))^2))/(length(((x-mean(x))) ^2)-1) And this seems to work, e.g., > my.var(V1) [1] 116.1 > var(V1) [1] 116.1 But when I try to see what the built-in var function does I get > var function (x, y = NULL, na.rm = FALSE, use) { if (missing(use)) use <- if (na.rm) "complete.obs" else "all.obs" na.method <- pmatch(use, c("all.obs", "complete.obs", "pairwise.complete.obs")) if (is.data.frame(x)) x <- as.matrix(x) else stopifnot(is.atomic(x)) if (is.data.frame(y)) y <- as.matrix(y) else stopifnot(is.atomic(y)) .Internal(cov(x, y, na.method, FALSE)) } <environment: namespace:stats> Being a novice, I can't understand what this means. I only have one variable, yet the code seems to be based on the covariance between x and y. What is y? Sorry for such a stupid question. I am just trying to figure out how R does things, and I can't seem to get my head around it. Thank you for your patience. -Ista Zahn http://izahn.homedns.org ______________________________________________ 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.
