stack

Shorthand for spread({ glue: true }). Children are glued together and their data-driven sizes sum into a continuous positional axis at this level. Used for stacked bar charts.

gf.chart(seafood, { axes: true })
  .flow(
    gf.spread({ by: "lake", dir: "x" }),
    gf.stack({ by: "species", dir: "y" })
  )
  .mark(gf.rect({ h: "count", fill: "species" }))
  .render(root, { w: 400, h: 250 });

Signature

// Operator form:
stack({ by?, dir, alignment?, ... })

// Combinator form:
stack({ dir, ... }, [m1, m2, ...])

Parameters

Same as spread without spacing or glue — stack always glues, so neither is configurable. Its by is the same path-aware option ("field", "datum.field" after a selection, a function, or a field(...) accessor); see spread → path-aware by. If you want gaps between children plus a continuous data axis, use spread({ spacing: N }) — spread's "data-driven SIZE composition" mode is the natural fit there.

size sets each entry's stack-axis extent (a field name, a field(...) accessor, or an explicit array). Set it to field(<name>).normalize() to make a stack a space-filling spine — its segments fill the extent in proportion to their share (the mosaic/marimekko conditional axis). See spread → Field-expression pipeline and spread → Space-filling spines.

Example

// Stacked bar chart grouped by "site", stacked by "variety"
.flow(
  spread({ by: "variety", dir: "x" }),
  stack({ by: "site", dir: "y" })
)