Is this easier? x.index <- duplicated(x.sample)==FALSE cbind(x.sample[x.index],y[x.index])
- Matt On 9/28/07, Marc Schwartz <[EMAIL PROTECTED]> wrote: > On Fri, 2007-09-28 at 17:48 -0400, Brian Perron wrote: > > Hello all, > > > > An elementary question that I am sure can be easily cracked by an R > > enthusiast. Let's say I have multiple scores (y) on subjects (x.sample). > > Some subjects have a few more scores than others. Can somebody suggest some > > code that will select the first score for each subject? > > > > For example, the following code generates scores for 5 subjects: > > > > > x <- c(1:5) > > > x.sample <- sample(x, 20, replace = TRUE) > > > x.sample <- sort(x.sample) > > > y <- rnorm(20) > > > z <- cbind(x.sample, y) > > > z > > > > x.sample y > > [1,] 1 -1.2006469 > > [2,] 1 0.7615261 > > [3,] 1 -0.1287516 > > [4,] 1 - 1.1796474 > > [5,] 1 -1.2902519 > > [6,] 2 -0.1614918 > > [7,] 2 -0.1464773 > > [8,] 2 -0.8875417 > > [9,] 2 0.3062891 > > [10,] 2 0.4398530 > > [11,] 3 -0.5717729 > > [12,] 3 - 0.2938118 > > [13,] 4 -0.2398887 > > [14,] 4 0.8425419 > > [15,] 4 2.5269801 > > [16,] 4 -0.3643613 > > [17,] 5 1.1690564 > > [18,] 5 -0.7644521 > > [19,] 5 1.4178982 > > [20,] 5 - 0.8198921 > > > > I am only interested in extracting the first score (y) for each unique > > subject (x.sample). So, I would like to generate the following output. > > > > x.sample y > > [1,] 1 -1.2006469 > > [2,] 2 -0.1614918 > > [3,] 3 -0.5717729 > > [4,] 4 -0.2398887 > > [5,] 5 1.1690564 > > > > Any assistance would be greatly appreciated. > > > > Regards, > > Brian > > See ?split, ?sapply and ?unique. > > Then try this: > > > cbind(unique(z[, 1]), sapply(split(z[, 2], z[, 1]), "[", 1)) > [,1] [,2] > 1 1 -1.2006469 > 2 2 -0.1614918 > 3 3 -0.5717729 > 4 4 -0.2398887 > 5 5 1.1690564 > > > The key part of that is: > > > split(z[, 2], z[, 1]) > $`1` > [1] -1.2006469 0.7615261 -0.1287516 -1.1796474 -1.2902519 > > $`2` > [1] -0.1614918 -0.1464773 -0.8875417 0.3062891 0.4398530 > > $`3` > [1] -0.5717729 -0.2938118 > > $`4` > [1] -0.2398887 0.8425419 2.5269801 -0.3643613 > > $`5` > [1] 1.1690564 -0.7644521 1.4178982 -0.8198921 > > > which splits 'z' by the values in the first column. > > Then we use sapply() to go through the list and subset the first element > in each vector: > > > sapply(split(z[, 2], z[, 1]), "[", 1) > 1 2 3 4 5 > -1.2006469 -0.1614918 -0.5717729 -0.2398887 1.1690564 > > > Then we cbind() that result to the unique values in the first column. > > HTH, > > Marc Schwartz > > ______________________________________________ > 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. > -- Matthew C Keller Postdoctoral Fellow Virginia Institute for Psychiatric and Behavioral Genetics ______________________________________________ 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.
