On Thu, May 24, 2012 at 08:24:38PM -0700, igorre25 wrote: > Hello, > > I need to build certain interpolation logic using R. Unfortunately, I just > started using R, and I'm not familiar with lots of advanced or just > convenient features of the language to make this simpler. So I struggled > for few days and pretty much reduced the whole exercise to the following > problem, which I cannot resolve: > > Assume we have a vector of some values with NA: > a <- c(1, 2, 3, NA, NA, 6, 7, NA, NA, 10) > > and some coefficients as a vector of the same length: > > f <- c(0.9, 1.1, 0.9, 1.1, 0.9, 1.1, 0.9, 1.1, 0.9, 1.1) > > I need to come up with function to get the following output > > o[1] = a[1] > o[2] = a[2] > o[3] = a[3] > o[4] = o[3]*[f3] # Because a[3] is NA > o[5] = o[4]*[f4] # Because a[4] is NA; This looks like recursive > calculations; If the rest of the elements we NA, I would use a * c(rep(1, > 3), cumprod(f[3:9])), but that's not the case > o[6] = a[6] # Not NA anymore > o[7] = a[7] > o[8] = o[7]*f[7] # Again a[8] is NA > o[9] = o[8]*f[8] > o[10] = a[10] # Not NA > > Even though my explanation may seems complex, in reality the requirement is > pretty simple and in Excel is achieved with a very short formula. > > The need to use R is to demonstrate capabilities of the language and then to > expand to more complex problems.
Hello: How is the output defined, if a[1] is NA? I think, you are not asking for a loop solution. However, in this case, it can be a reasonable option. For example a <- c(1, 2, 3, NA, NA, 6, 7, NA, NA, 10) f <- c(0.9, 1.1, 0.9, 1.1, 0.9, 1.1, 0.9, 1.1, 0.9, 1.1) n <- length(a) o <- rep(NA, times=n) prev <- 1 for (i in 1:n) { if (is.na(a[i])) { o[i] <- f[i]*prev } else { o[i] <- a[i] } prev <- o[i] } A more straightforward translation of the Excel formulas is getCell <- function(i) { if (i == 0) return(1) if (is.na(a[i])) { return(f[i]*getCell(i-1)) } else { return(a[i]) } } x <- rep(NA, times=n) for (i in 1:n) { x[i] <- getCell(i) } identical(o, x) # [1] TRUE Petr Savicky. ______________________________________________ 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.