R/moveMe.R

In mrdwab/SOfun: Functions From Answers to R Questions on Stack Overflow

#' Reorders the Contents of a Vector
#' 
#' Shuffle the order of a vector around using natural language statements.
#' 
#' This can be a useful function for reordering the columns of a
#' \code{data.frame} or \code{data.table} in a convenient manner. In such
#' cases, the \code{invec} would be \code{names(your_data_frame)}. When using
#' \code{data.table}s, remember to use \code{setcolorder} to avoid copying.
#' 
#' The \code{movecommand} argument is specified in the form of \code{"a, b
#' before f"}. The positions to move are: \itemize{ \item \strong{first}: move
#' the specified items to the first postion. \item \strong{last}: move the
#' specified items to the last position. \item \strong{before}: move the
#' specified items before the value mentioned. \item \strong{after}: move the
#' specified items after the value mentioned. } Multiples are allowed:
#' \itemize{ \item Specify multiple values to be moved by separating them with
#' a comma. \item Chain multiple move commands by separating them with a
#' semicolon. }
#' 
#' @param invec The input vector
#' @param movecommand The command that describes how you want to shuffle the
#' vector. See \emph{Details}.
#' @return A vector.
#' @author Ananda Mahto
#' @references \url{http://stackoverflow.com/a/18420673/1270695}
#' @examples
#' 
#' myvec <- letters[1:10]
#' myvec
#' moveMe(myvec, "a last; b, e, g before d; c first; h after j")
#' 
#' x <- names(mtcars)
#' x
#' moveMe(x, "hp first; cyl after drat; vs, am, gear before mpg; wt last")
#' 
#' @export moveMe
moveMe <- function(invec, movecommand) {
  movecommand <- lapply(strsplit(strsplit(movecommand, ";")[[1]], ",|\\s+"), 
                        function(x) x[x != ""])
  movelist <- lapply(movecommand, function(x) {
    Where <- x[which(x %in% c("before", "after", "first", "last")):length(x)]
    ToMove <- setdiff(x, Where)
    list(ToMove, Where)
  })
  myVec <- invec
  for (i in seq_along(movelist)) {
    temp <- setdiff(myVec, movelist[[i]][[1]])
    A <- movelist[[i]][[2]][1]
    if (A %in% c("before", "after")) {
      ba <- movelist[[i]][[2]][2]
      if (A == "before") {
        after <- match(ba, temp)-1
      } else if (A == "after") {
        after <- match(ba, temp)
      }    
    } else if (A == "first") {
      after <- 0
    } else if (A == "last") {
      after <- length(myVec)
    }
    myVec <- append(temp, values = movelist[[i]][[1]], after = after)
  }
  myVec
}
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