support dagitty objects

DESCRIPTION

@@ -33,6 +33,7 @@ Suggests:
     ape,
     covr,
     data.tree,
+    dagitty,
     graph,
     influenceR,
     methods,

NAMESPACE

@@ -10,6 +10,7 @@ S3method(as.data.frame,tbl_graph)
 S3method(as.igraph,tbl_graph)
 S3method(as.list,tbl_graph)
 S3method(as_tbl_graph,Node)
+S3method(as_tbl_graph,dagitty)
 S3method(as_tbl_graph,data.frame)
 S3method(as_tbl_graph,default)
 S3method(as_tbl_graph,dendrogram)
@@ -593,11 +594,13 @@ importFrom(rlang,.data)
 importFrom(rlang,UQS)
 importFrom(rlang,as_quosure)
 importFrom(rlang,caller_env)
+importFrom(rlang,check_installed)
 importFrom(rlang,enexpr)
 importFrom(rlang,enquo)
 importFrom(rlang,eval_bare)
 importFrom(rlang,eval_tidy)
 importFrom(rlang,is_bare_list)
+importFrom(rlang,is_empty)
 importFrom(rlang,list2)
 importFrom(rlang,quo)
 importFrom(rlang,quo_text)

R/dagitty.R

@@ -0,0 +1,34 @@
+#' @describeIn tbl_graph Method to deal with dagitty objects from the dagitty package
+#' @export
+#' @importFrom rlang is_empty check_installed
+as_tbl_graph.dagitty <- function(x, directed = TRUE, ...) {
+  check_installed('dagitty', 'in order to coerce a dagitty object to tbl_graph')
+  if (is_empty(names(x))) return(create_empty(0))
+
+  nodes <- tibble::tibble(
+    name = names(x)
+  )
+  adjusted <- dagitty::adjustedNodes(x)
+  if (!is_empty(adjusted)) nodes$adjusted <- nodes$name %in% adjusted
+  exposure <- dagitty::exposures(x)
+  if (!is_empty(exposure)) nodes$exposure <- nodes$name %in% exposure
+  outcome <- dagitty::outcomes(x)
+  if (!is_empty(outcome)) nodes$outcome <- nodes$name %in% outcome
+  latent <- dagitty::latents(x)
+  if (!is_empty(latent)) nodes$latent <- nodes$name %in% latent
+  coords <- dagitty::coordinates(x)
+  if (!all(is.na(coords$x))) {
+    nodes$x <- coords$x
+    nodes$y <- coords$y
+  }
+
+  e <- dagitty::edges(x)
+  if (is_empty(e)){
+    e <- tibble::tibble(from = integer(), to = integer())
+  } else {
+    e <- e[c('v', 'w', 'e')]
+    names(e) <- c('from', 'to', 'type')
+  } 
+
+  tbl_graph(nodes = nodes, edges = e, directed = directed)
+}