R/extract1.R

In sticky: Persist Attributes Across Data Operations

#' Extract
#'
#' @param x sticky; object to extract from
# @param i values to extract
#' @param ... additional parameters
#'
#' @details
#'
#' Implements `[` for sticky attributes. This methods ensures that existing
#' attributes are propagated forward.
#'
#' @seealso
#'   \code{\link[base]{attributes}}, specifically \code{mostattributes}
#'
#' @rdname extract1
#' @export
#' @include sticky.R


`[.sticky` <- function(x,...) {

  r <- NextMethod("[")

  has_dim <- has_attr(r, 'dim')
  r_dim <- dim(r)

  #' When `[`` produces a different class, drop=TRUE
  #' We should only copy attributes when the

  cls_x <- setdiff( class(x), 'sticky' )
  cls_r <- setdiff( class(r), 'sticky' )

  if(
    all( cls_r %in% cls_x )
    # length( cls_x ) == length( cls_r ) &&  # all( cls_r %in% cls_x )
    # all( cls_x == cls_r )
  )
    mostattributes(r) <- attributes(x)

  if( has_dim ) dim(r) <- r_dim

  r
}