Sankey flow diagram layer (sugar) — mark

Creates a Sankey diagram showing directed flows between nodes. Equivalent to the pipeline as_graph() |> layout_sankey() |> mark_polygon(data = ~ribbons) |> mark_rect(data = ~nodes) – see §3.3.4a. Accepts an edges table with source, target, and optionally value columns (either mapped via structural aesthetics or present as literal columns); node and ribbon geometry come from the built-in layered layout (deterministic, dependency-free). The derived flow/node fill channel defaults to source identity and ships with the curated token palette – friendly qualitative for categories, viridis sequential for continuous values; chain scale_fill() to replace it (last call wins).

Usage

mark_sankey(
  plot,
  mapping = NULL,
  data = NULL,
  ...,
  node_color = ._MARK_STYLE$ink,
  edge_alpha = ._MARK_STYLE$alpha_link,
  show_labels = TRUE
)

Arguments

plot: A plotit object
mapping: Structural aesthetics: source (required), target (required), value (optional). Visual: fill colours ribbons and nodes alike; ribbons default to source identity.
data: Optional edges data.frame for this layer
...: Unused; fine-tuning (padding, curvature, node width) lives on layout_sankey() in the explicit pipeline form.
node_color: Default colour for node rectangles (used when no fill mapping is present, default ._MARK_STYLE$ink = "grey30").
edge_alpha: Alpha transparency for flow ribbons (default ._MARK_STYLE$alpha_link = 0.5).
show_labels: If TRUE (default), draw node ids inside the strips.

Value

Modified plotit object; @graph holds the laid-out tables.

Details

The laid-out graph (nodes / edges / ribbons tables) is stored on @graph, so subsequent marks can reference any table directly for tuning beyond this sugar's two parameters.

References

AntV G2: Sankey (graphlib)

Examples

df <- data.frame(
  source = c("A", "A", "B", "B", "C"),
  target = c("B", "C", "C", "D", "D"),
  value  = c(10, 5, 8, 3, 6)
)
df |>
  plotit(encode(
    source = source, target = target,
    value = value, fill = source
  )) |>
  mark_sankey() |>
  scale_fill(range = "viridis")
#> Coordinate system already present.
#> ℹ Adding new coordinate system, which will replace the existing one.
#> Scale for fill is already present.
#> Adding another scale for fill, which will replace the existing scale.