--- a
+++ b/R/GatherGraphNode.R
@@ -0,0 +1,54 @@
+#' Gather graph nodes from a data frame
+#' Please note that this function is from the 'ggraph' package and has not been altered in functionality,
+#' but it has been optimized and iterated.
+#' It is not original content of 'TransProR'.
+#' However, since 'ggraph' caused frequent GitHub Action errors during the creation of 'TransProR',
+#' the author directly referenced the involved functions in 'TransProR'.
+#' This is not the author's original creation. All users please be aware!
+#' @inheritParams gather_graph_edge
+#' @param value Column name used for summarizing node size, defaults to the last column
+#' @return a tibble of graph nodes
+#' @export
+#' @importFrom dplyr group_by summarise mutate bind_rows n all_of across
+#' @importFrom tidyr unite
+#' @importFrom tibble as_tibble
+#' @importFrom utils tail
+gather_graph_node <- function(df, index = NULL, value = utils::tail(colnames(df), 1), root = NULL) {
+  if (length(index) < 2) {
+    stop("Please specify at least two index columns.")
+  } else {
+    nodes_list <- lapply(seq_along(index), function(i) {
+      dots <- index[1:i]
+      df %>%
+        dplyr::group_by(dplyr::across(dplyr::all_of(dots))) %>%
+        dplyr::summarise(node.size = sum(.data[[value]], na.rm = TRUE),
+                         node.level = index[i],
+                         node.count = dplyr::n(), .groups = 'drop') %>%
+        dplyr::mutate(node.short_name = as.character(.data[[dots[length(dots)]]]),
+                      node.branch = as.character(.data[[dots[1]]])) %>%
+        tidyr::unite(col = "node.name", all_of(dots), sep = "/")
+    })
+
+    nodes <- dplyr::bind_rows(nodes_list) %>%
+      tibble::as_tibble()
+
+    nodes$node.level <- factor(nodes$node.level, levels = index)
+
+    if (!is.null(root)) {
+      root_data <- data.frame(
+        node.name = root,
+        node.size = sum(df[[value]], na.rm = TRUE),
+        node.level = root,
+        node.count = 1,
+        node.short_name = root,
+        node.branch = root,
+        stringsAsFactors = FALSE
+      )
+
+      nodes <- dplyr::bind_rows(root_data, nodes)
+      nodes$node.level <- factor(nodes$node.level, levels = c(root, index))
+    }
+
+    return(nodes)
+  }
+}