Hi, On Wed, Jun 3, 2015 at 8:26 AM, Thomas Chesney <thomas.ches...@nottingham.ac.uk> wrote: > I'd like to add some columns into the middle of this: > > vec <- c(1, -1) > lst <- lapply(numeric(n-1), function(x) vec) > combos <- as.matrix(expand.grid(lst)) > colnames(combos) <- NULL
This isn't quite reproducible, since n is undefined. I substituted numeric(6), since that gives the right number of columns. I'd take advantage of R's habit (bug or feature? your call!) of repeating items as needed: combos2 <- cbind(0, combos[, 1:3], 0, combos[, 4:6], 0) > The way I have used is: > > combos2 <- matrix(NA, nrow=64, ncol=9) > combos2[,1] <- 0 > combos2[,2] <- combos[,1] > combos2[,3] <- combos[,2] > combos2[,4] <- combos[,3] > combos2[,5] <- 0 > combos2[,6] <- combos[,4] > combos2[,7] <- combos[,5] > combos2[,8] <- combos[,6] > combos2[,9] <- 0 > > But I guess there is an easier way - is there a way to simply insert new > columns into combos? > > BTW I know I could have shortened this a bit to: > > combos2[,2:4] <- combos[,1:3] > > ========== > > Also can anyone recommend a good source to explain my combos data type? I > don't fully understand all the output of this: > > str(combos) > num [1:64, 1:6] 1 -1 1 -1 1 -1 1 -1 1 -1 ... > - attr(*, "dimnames")=List of 2 > ..$ : NULL > ..$ : NULL Well, take a careful look. The first line tells you that your matrix is numeric (matrices can only contain elements of one type), that it has 64 rows and 6 columns, and a bit of what the contents look like. The second line tells you that your matrix has as attributes a list of two dimnames, and the subsequent lines tell you that both row and column names are NULL (because you set them that way!) Try, for example, str(data.frame(combos)) and compare. Working through the examples in ?str might also help. Sarah > Thank you, > > Thomas Chesney > > > ______________________________________________ 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.
