guide_edge_direction: Edge direction guide
In YTLogos/ggraph: An Implementation of Grammar of Graphics for Graphs and Networks

Description Usage Arguments Examples

This guide is intended to show the direction of edges based on the aesthetics mapped to its progression, such as changing width, colour and opacity.

guide_edge_direction(title = waiver(), title.position = NULL,
  title.theme = NULL, title.hjust = NULL, title.vjust = NULL,
  arrow = TRUE, arrow.position = NULL, barwidth = NULL,
  barheight = NULL, nbin = 500, direction = NULL, default.unit = "line",
  reverse = FALSE, order = 0, ...)

`title`	A character string or expression indicating a title of guide. If `NULL`, the title is not shown. By default (`waiver`), the name of the scale object or the name specified in `labs` is used for the title.
`title.position`	A character string indicating the position of a title. One of "top" (default for a vertical guide), "bottom", "left" (default for a horizontal guide), or "right."
`title.theme`	A theme object for rendering the title text. Usually the object of `element_text` is expected. By default, the theme is specified by `legend.title` in `theme` or theme.
`title.hjust`	A number specifying horizontal justification of the title text.
`title.vjust`	A number specifying vertical justification of the title text.
`arrow`	Logical. Should an arrow be drawn to illustrate the direction. Defaults to `TRUE`
`arrow.position`	The position of the arrow relative to the example edge.
`barwidth`	A numeric or a `unit` object specifying the width of the colorbar. Default value is `legend.key.width` or `legend.key.size` in `theme` or theme.
`barheight`	A numeric or a `unit` object specifying the height of the colorbar. Default value is `legend.key.height` or `legend.key.size` in `theme` or theme.
`nbin`	A numeric specifying the number of bins for drawing colorbar. A smoother colorbar for a larger value.
`direction`	A character string indicating the direction of the guide. One of "horizontal" or "vertical."
`default.unit`	A character string indicating `unit` for `barwidth` and `barheight`.
`reverse`	logical. If `TRUE` the colorbar is reversed. By default, the highest value is on the top and the lowest value is on the bottom
`order`	positive integer less that 99 that specifies the order of this guide among multiple guides. This controls the order in which multiple guides are displayed, not the contents of the guide itself. If 0 (default), the order is determined by a secret algorithm.
`...`	ignored.

gr <- igraph::graph_from_data_frame(highschool)
ggraph(gr, layout = 'kk') +
  geom_edge_fan(aes(alpha = ..index..)) +
  guides(edge_alpha = guide_edge_direction())