Some scale_edge_* only work when ggraph is loaded

[Ax3man]

It appears some scales only work when ggraph is actually loaded. When referring to them with :: the correct guide cannot be found. When the guide is manually specified, the scale does work (with a warning), but no guide is shown.

data('highschool', package = 'ggraph')
graph <- igraph::graph_from_data_frame(highschool)

ggraph::ggraph(graph, layout = 'kk') + 
  ggraph::geom_edge_link(ggplot2::aes(color = year)) + 
  ggraph::scale_edge_color_gradient()
# Error in get(as.character(FUN), mode = "function", envir = envir) : 
#   object 'guide_edge_colourbar' of mode 'function' was not found

ggraph::ggraph(graph, layout = 'kk') + 
  ggraph::geom_edge_link(ggplot2::aes(color = year)) + 
  ggraph::scale_edge_color_gradient(guide = ggraph::guide_edge_colorbar())
# Warning message:
#   In guide_train.colorbar(guide, scale) :
#   colorbar guide needs colour or fill scales.

These examples do work after library(ggraph).

I believe this will be a problem for code in packages, as requireNamespace does not appear to alleviate the problem.

[thomasp85]

This is an unfortunate result of how scale extensions are made in ggplot2 and outside the reach of ggraph or any other extension package. The solution is to import and reexport the needed function in your own package...

[Ax3man]

Ok, that solution is fine. For future visitors, including this solved it for me (using roxygen):

#' @importFrom ggraph guide_train.edge_colourbar
#' @export
ggraph::guide_train.edge_colourbar

Thanks Thomas!

[thomasp85]

Thanks @Ax3man

[llrs]

I don't know if it is the way I use packages, but I thought I couldn't modify the color gradient of edges because I didn't see anything in their vignette. Thank for mentioning this here (as well as on #25) !