I need to produce a network graph where (A) some nodes are a subcategory of other nodes, (B) some nodes are considered equivalent to other nodes, and (C) some nodes are specifically highlighted as being especially distinct from other nodes. Edges showing relationship A might have a uni-directional arrow (i.e., an arrowhead at only one end of the edge). Edges showing relationship B might have bi-directional arrows (i.e., an arrowhead at each end of the edge), or might have no arrowheads at all. Edges showing relationship C might be shown in a distinct color, or might be dashed, or might have opposing arrowheads along the edge, etc. For the sake of argument, let’s say that for relationships of type B I wanted an arrowhead at each end of the relevant edge. How would I go about doing that with visNetwork?

Simon Larson previously answered a similar question in the sole response to this post. He proposed setting individual arrow types in the edges data frame by adding columns arrows.to.type and arrows.from.type, as shown in the following example:

library(visNetwork)
library(magrittr)

nodes <- data.frame(id=c("a","b","c","d"), label=c("a","b","c","d"))
edges <- data.frame(
  from = c("a","a","a"),
  to = c("b","c","d"),
  arrows.from.type = c(NA,"circle","circle"),
  arrows.to.type = c("arrow","circle",NA)
)

visNetwork(nodes, edges)

In his response, the above code produced this network graph, which has the expected arrows and circles at the edge end-points:
enter image description here

When I run the above code, I get the following network graph, which has no arrows or circles at the edge end-points:
enter image description here

Any idea why I’m not getting the desired result? Additionally, I’d be open to hearing other means of graphing the types of relationships I described, though I’d still be grateful to figure out how to show the bi-directional edge.