Ggraph: Incorrect edge attributes depending on loops and end_cap

[daniel-munro]

This seems related to #62, but that issue was closed and I'm seeing this in version 1.0.1.

The below example contains a loop and specifies end_cap for the edges, and one of the edges is the wrong color. The next examples show that it plots correctly when the loop is replaced with a non-loop edge, when the loop is listed after the other edges, and when end_cap is not specified.

The problem persists when using an undirected graph, when using geom_edge_link or geom_edge_arc instead of geom_edge_fan, and when omitting the geom_edge_loop call.

library(ggraph)
library(igraph)

## Incorrect when loop listed first
d <- data.frame(node1 = c('C', 'A', 'B'),
                node2 = c('C', 'B', 'A'),
                value = c('Y', 'X', 'X'))
g <- graph_from_data_frame(d, directed = TRUE)
ggraph(g, layout = 'nicely') +
  geom_edge_fan(aes(color = value),
                end_cap = circle(5, 'mm')) +
  geom_edge_loop(aes(color = value)) +
  geom_node_label(aes(label = name))

## Correct when no loop
d <- data.frame(node1 = c('C', 'A', 'B'),
                node2 = c('D', 'B', 'A'),
                value = c('Y', 'X', 'X'))
g <- graph_from_data_frame(d, directed = TRUE)
ggraph(g, layout = 'nicely') +
  geom_edge_fan(aes(color = value),
                end_cap = circle(5, 'mm')) +
  geom_edge_loop(aes(color = value)) +
  geom_node_label(aes(label = name))

## Correct when loop listed third
d <- data.frame(node1 = c('A', 'B', 'C'),
                node2 = c('B', 'A', 'C'),
                value = c('X', 'X', 'Y'))
g <- graph_from_data_frame(d, directed = TRUE)
ggraph(g, layout = 'nicely') +
  geom_edge_fan(aes(color = value),
                end_cap = circle(5, 'mm')) +
  geom_edge_loop(aes(color = value)) +
  geom_node_label(aes(label = name))

## Correct when no end_cap specified
d <- data.frame(node1 = c('C', 'A', 'B'),
                node2 = c('C', 'B', 'A'),
                value = c('Y', 'X', 'X'))
g <- graph_from_data_frame(d, directed = TRUE)
ggraph(g, layout = 'nicely') +
  geom_edge_fan(aes(color = value)) +
  geom_edge_loop(aes(color = value)) +
  geom_node_label(aes(label = name))

[jhrcook]

I am also having a problem with the edge attribute edge_alpha sometimes being misplaced when specifying end_cap or start_cap to anything besides 0. Below is the end_cap and start_cap set to 0 with the edges coming from the green node to the two blue nodes weighted correctly:

Below is the result of only changing end_cap and start_cap to 2. The red arrow points at the misplaced edge attribute:

I can provide more detail if requested.

[rcannood]

I can confirm this. Seems to be related to #150. I'm using ggraph 1.0.2.

I can reproduce the bug with the code below. In this plot, loop A→A is missing; edge A→B is missing its start_cap, and A→B should be coloured blue.

library(tidyverse)
library(tidygraph)
library(ggraph)

edges <-
  tribble(
    ~from, ~to, ~effect,
    "A", "A", "red",
    "A", "B", "blue"
  )

set.seed(1)
ggraph(tbl_graph(edges = edges), layout = "nicely") +
  geom_edge_fan(
    aes(colour = effect), 
    start_cap = circle(30, "mm"), end_cap = circle(30, "mm"),
    arrow = grid::arrow(type = "closed")
  ) + 
  geom_node_circle() +
  geom_node_text(aes(label = name)) +
  scale_edge_colour_identity()

If I remove the self loop from the tibble, the bug does not occur.

edges <-
  tribble(
    ~from, ~to, ~effect,
    "A", "B", "blue"
  )

set.seed(1)
ggraph(tbl_graph(edges = edges), layout = "nicely") +
  geom_edge_fan(
    aes(colour = effect), 
    start_cap = circle(30, "mm"), end_cap = circle(30, "mm"),
    arrow = grid::arrow(type = "closed")
  ) + 
  geom_node_circle() +
  geom_node_text(aes(label = name)) +
  scale_edge_colour_identity()

If I remove the start_cap and end_cap, the problem also does not occur.

edges <-
  tribble(
    ~from, ~to, ~effect,
    "A", "A", "red",
    "A", "B", "blue"
  )

set.seed(1)
ggraph(tbl_graph(edges = edges), layout = "nicely") +
  geom_edge_fan(
    aes(colour = effect), 
    arrow = grid::arrow(type = "closed")
  ) + 
  geom_node_circle() +
  geom_node_text(aes(label = name)) +
  scale_edge_colour_identity()

[rcannood]

Here is a workaround, by filtering out self loops in geom_edge_fan() using the filter aesthetic (Thanks @zouter).

library(tidyverse)
library(tidygraph)
library(ggraph)

edges <-
  tribble(
    ~from, ~to, ~effect,
    "A", "A", "red",
    "A", "B", "blue"
  )

set.seed(1)
ggraph(tbl_graph(edges = edges), layout = "nicely") +
  geom_edge_loop(
    aes(colour = effect), 
    start_cap = circle(30, "mm"), end_cap = circle(30, "mm"),
    arrow = grid::arrow(type = "closed")
  ) + 
  geom_edge_fan(
    aes(colour = effect, filter = from != to), 
    start_cap = circle(30, "mm"), end_cap = circle(30, "mm"),
    arrow = grid::arrow(type = "closed")
  ) + 
  geom_node_circle(aes(r = .08)) +
  geom_node_text(aes(label = name)) +
  scale_edge_colour_identity()

[rcannood]

@thomasp85 : I hope the example and the workaround shown above can help you get to the bottom of this.

[thomasp85]

I am not able to reproduce any of your problems, but the edge-capping stuff is pretty involved so maybe it's something on my end.

Can I get one of you to upgrade to the latest development version and see if you can provoke this bug to appear again and if so, post (another) reprex?

[daniel-munro]

I tried it in the latest development version and no longer see the bug, for any of the cases I had mentioned.

[thomasp85]

Thanks for confirming... I made a lot of fixes a year or so ago but apparently didn't close all affected issues. Will close this

[rcannood]

@thomasp85 This problem still occurs on the CRAN version of ggraph. When are you planning to push these fixes to CRAN?

[thomasp85]

Yes they do... I'm currently working on a new release which will include this fix. I can't give you an ETA, but soon... In the meantime just install from GitHub

[rcannood]

I'm currently working on a new release

Alright thanks! :+1:

In the meantime just install from GitHub

I can't seem to convince CRAN to let me include Remotes: thomasp85/ggraph in my packages, so this is a little difficult :wink: I'll just wait a little until the update hits CRAN.

[thomasp85]

Ah, yes — if you are waiting because of a package release of your own you'll just have to be patient

[rcannood]

I noticed the new release of ggraph on CRAN. Thanks for your hard work! :)