Cannot create data frame column for tbl_graph class

[JosiahParry]

With an object of class tbl_graph it is not possible to create a data frame column. However, it is possible to do so with a normal data frame. This would be a welcomed addition to tidygraph functionality.

library(dplyr)
library(tidygraph)

nn <- create_star(10, directed = TRUE, mutual = TRUE)

# this should work
nn |> 
  mutate(id = row_number(),
         df = .N())
#> Error in `vertex.attributes<-`(graph, index = index, value = value): Invalid attribute value length, must match number of vertices

# cast as data.frame
nn_df <- nn |> 
  mutate(id = row_number()) |> 
  as_tibble()

# create data.frame column
nn_df |> 
  mutate(df = nn_df)
#> # A tibble: 10 × 2
#>       id df$id
#>    <int> <int>
#>  1     1     1
#>  2     2     2
#>  3     3     3
#>  4     4     4
#>  5     5     5
#>  6     6     6
#>  7     7     7
#>  8     8     8
#>  9     9     9
#> 10    10    10

^{Created on 2022-08-16 by the reprex package (v2.0.1)}

[thomasp85]

This is sadly a limitation of igraph which is used as the internal data structure. I'm not sure they'd be willing to add this complexity to the code base. What say you @gaborcsardi?

[gaborcsardi]

I am not sure I follow. nn is not a data frame, so you cannot call mutate() on it. Are you saying that a graph should be a data frame?

[thomasp85]

This is tidygraph syntax... but the underlying limitation described here is that igraph node and edge attributes cannot be a dataframe

[gaborcsardi]

I don't remember such limitation, I thought they could be generic R objects:

library(igraph)
g <- make_star(10)
va <- replicate(10, mtcars, simplify = FALSE)
V(g)$foo  <- va
g

#> IGRAPH ff30718 D--- 10 9 -- In-star
#> + attr: name (g/c), mode (g/c), center (g/n), foo (v/x)
#> + edges from ff30718:
#> [1]  2->1  3->1  4->1  5->1  6->1  7->1  8->1  9->1 10->1

[thomasp85]

They can be lists, but they can't be a data.frame with the rows in the data frame corresponding to the vertices/edges