R/nodes.R

In ggraph: An Implementation of Grammar of Graphics for Graphs and Networks

#' Create a node extractor function
#'
#' This function returns another function that can extract nodes from a
#' ggraph_layout object. As a ggraph_layout object is essentially a data.frame
#' of nodes it might seem useless to provide this function, but since the node
#' data is not necessarily available until after the `ggraph()` call it
#' can be beneficial to be able to add information to the node data on a
#' per-layer basis. Unlike [get_edges()] the use of `get_nodes` is not
#' mandatory and is only required if additional data should be added to selected
#' node layers.
#'
#' @param ... Additional data that should be cbind'ed together with the node
#' data. Accepts expressions that will be evaluated on the node data in it's
#' original order (irrespective of any reordering by the layout)
#'
#' @return A data.frame with the node data as well of any additional data
#' supplied through `...`
#'
#' @family extractors
#'
#' @export
#'
get_nodes <- function(...) {
  dots <- enquos(...)
  function(layout) {
    layout_reorder <- layout[order(layout$.ggraph.orig_index), ]
    extra_data <- lapply(dots, function(x) {
      val <- eval_tidy(x, layout_reorder)
      rep(val, length.out = nrow(layout))[layout$.ggraph.orig_index]
    })
    if (length(extra_data) > 0) {
      layout <- cbind(
        layout,
        data_frame0(!!!extra_data)
      )
    }
    attr(layout, 'type_ggraph') <- 'node_ggraph'
    layout
  }
}