R/head2.R

In popbio: Construction and Analysis of Matrix Population Models

#' Return the first and last part of a matrix or dataframe
#'
#' Returns the first and last rows using output from both \code{\link{head}} and
#' \code{\link{tail}} and separates the two parts with dots. Useful for viewing
#' ordered datasets such as longitudinal census data.
#'
#' @param x A matrix or dataframe
#' @param head The number of first rows
#' @param tail The number of last rows
#' @param dotrows The number of rows of dots
#'
#' @return A smaller object with first and last rows only
#'
#' @author Chris Stubben
#'
#' @examples
#' head2(aq.trans)
#'
#' @export

head2 <- function(x, head = 3, tail = 1, dotrows = 1) {
  if (!(is.matrix(x) || is.data.frame(x))) {
    stop("A data frame or matrix is required")
  }
  # check number of rows in matrix or dataframe
  if (nrow(x) < head + dotrows + tail) {
    x
  }
  else {
    ## fix -- tail adds rownames to matrix using addrownums, but not head
    h1 <- head(x, head + dotrows)
    if (is.null(rownames(h1))) {
      rownames(h1) <- paste("[", 1:(head + dotrows), ",]", sep = "")
    }
    x <- format(rbind(h1, tail(x, tail)))
    if (dotrows > 0) {
      x[(head + 1):(head + dotrows), ] <- "."
      for (i in 1:dotrows) {
        rownames(x)[head + i] <- paste(".", substring("         ", 1, i - 1))
      }
    }
    ## remove quotes from matrix elements?
    noquote(x)
  }
}