moved the external graphing packages to Suggested in order to trim the dependencies

R-package/R/xgb.plot.tree.R

@@ -15,7 +15,6 @@
 #' @importFrom stringr str_split
 #' @importFrom stringr str_extract
 #' @importFrom stringr str_trim
-#' @importFrom DiagrammeR mermaid
 #' @param feature_names names of each feature as a character vector. Can be extracted from a sparse matrix (see example). If model dump already contains feature names, this argument should be \code{NULL}.
 #' @param filename_dump the path to the text file storing the model. Model dump must include the gain per feature and per tree (parameter \code{with.stats = T} in function \code{xgb.dump}). Possible to provide a model directly (see \code{model} argument).
 #' @param model generated by the \code{xgb.train} function. Avoid the creation of a dump file.
@@ -64,7 +63,11 @@ xgb.plot.tree <- function(feature_names = NULL, filename_dump = NULL, model = NU
   if (!class(model) %in% c("xgb.Booster", "NULL")) {
     stop("model: Has to be an object of class xgb.Booster model generaged by the xgb.train function.")
   }
-    
+  
+  if (!requireNamespace("DiagrammeR", quietly = TRUE)) {
+    stop("DiagrammeR package is required for xgb.plot.tree", call. = FALSE)
+  }
+  
   if(is.null(model)){
     allTrees <- xgb.model.dt.tree(feature_names = feature_names, filename_dump = filename_dump, n_first_tree = n_first_tree)  
   } else {
@@ -85,7 +88,7 @@ xgb.plot.tree <- function(feature_names = NULL, filename_dump = NULL, model = NU
   no <- allTrees[Feature!="Leaf", c(No)] %>% paste(collapse = ",") %>% paste("class ", ., " redNode", sep = "")
   
   path <- allTrees[Feature!="Leaf", c(yesPath, noPath)] %>% .[order(.)] %>% paste(sep = "", collapse = ";") %>% paste("graph LR", .,collapse = "", sep = ";") %>% paste(CSSstyle, yes, no, sep = ";")
-  mermaid(path, width, height)
+  DiagrammeR::mermaid(path, width, height)
 }
 
 # Avoid error messages during CRAN check.