Cannot set sender and receiver in tbl_graph about tidygraph

[michaellevy]

Creating the network via igraph::graph_from_edgelist and the converting works as expected:

igraph::graph_from_edgelist(as.matrix(el)) %>%
  as_tbl_graph()

[thomasp85]

Try setting directed = TRUE in tbl_graph?

[michaellevy]

directed = TRUE is documented as the default. I confirmed it doesn't change the result.

[thomasp85]

Ok - this was a “From-my-phone” suggestion, sorry for leading you astray.

I’ll look into it

[michaellevy]

No worries. It's easy enough to create and convert the igraph object, so it's not blocking me. Just fyi.

[ramorel]

Problem seems to occur in the as_graph_node_edge method when dealing with a tibble. Note first that when using a data frame, the problem does not occur (provided stringsAsfactors = F):

> el <- data.frame(from = c("b", "c"), to = c("a", "b"), stringsAsFactors = F)
> nodes <- data.frame(name = letters[1:3], stringsAsFactors = F)
> tbl_graph(nodes, el)
# A tbl_graph: 3 nodes and 2 edges
#
# A rooted tree
#
# Node Data: 3 x 1 (active)
  name 
  <chr>
1 a    
2 b    
3 c    
#
# Edge Data: 2 x 2
   from    to
  <int> <int>
1     2     1
2     3     2

The issue occurs in the as_graph_node_edge when the method evaluates whether the edgelist columns are of class character. Currently, the evaluation reads: if (is.character(edges[, 1])) and then proceeds to match the edgelist names to the node names. If edges is a tibble, this will always evaluate to false, since the subset edges[, 1] produces a one column tibble and not a vector of characters.

> el <- data.frame(from = c("b", "c"), to = c("a", "b"), stringsAsFactors = F)
> class(el[, 1])
[1] "character"
> el <- tibble(from = c("b", "c"), to = c("a", "b"))
> class(el[, 1])
[1] "tbl_df"     "tbl"        "data.frame"

As a result, the matching of the names between the edgelist and nodes list does not occur, since if (is.character(edges[, 1])) evaluates to false. If the evaluation uses double bracket notation-- if (is.character(edges[[1]])) -- it evaluates to true and the matching occurs.

> el <- tibble(from = c("b", "c"), to = c("a", "b"))
> class(el[[1]])
[1] "character"

Replacing the single bracket notation for double bracket notation in as_graph_node_edge solves the problem.

[ramorel]

I have filed a pull request fixing the issue. This is my very first pull request. I hope I have done it well and the request is clear 😬. #53

[thomasp85]

Thanks @ramorel - much appreciated!

The PR was well explained and executed - Congrats on becoming a contributor 🎉