mark

Sets the visual mark drawn for each data item — the shape that turns rows into pixels.

from gofish import chart, spread, rect

chart(seafood, axes=True).flow(spread(by="lake", dir="x")).mark(
    rect(h="count")
).render(w=500, h=300)

Signature

ChartBuilder.mark(mark) -> ChartBuilder

Parameters

Parameter	Type	Description
mark	Mark | ChartBuilder | callable	A mark factory result, a nested chart(...) drawn per group, or a (data) -> ChartBuilder

Returns a new ChartBuilder with the mark set.

Mark types

Mark	Draws
rect	A rectangle per item
circle	A circle per item
ellipse	An ellipse per item
line	A line through the items
ribbon	A filled area through the items
blank	An invisible positioning guide

Encoding channels

Mark options accept either a constant or a field name (a string matching a column in your data):

rect(h="count", fill="species")  # height and color from data fields
rect(h="count", fill="#4e79a7")  # height from data, constant color

Naming marks

Call .name("layerName") on a mark so another chart can reference it with ref / selectAll:

chart(data).flow(scatter(by="lake", x="x", y="y")).mark(blank().name("points"))

Nested chart as a mark

mark() also accepts a whole nested chart(...) — one sub-chart drawn per group (a pie glyph per scatter point, a small multiple per facet). Leave the nested chart's data off and it inherits the incoming partition (the group's rows), so you don't thread the data through a callback:

chart(catch_locations).flow(scatter(by="lake", x="x", y="y")).mark(
    chart(coord=clock())  # no data -> inherits this lake's partition
    .flow(stack(by="species", dir="x", h=20))
    .mark(rect(w="count", fill="species"))
)

A no-data chart() / chart(**options) is an empty scope: as a mark(...) it binds the incoming group, and inside .layer(...) it binds the previous tier's marks.

The older callback form mark(lambda data: chart(data, ...).flow(...).mark(...)) still works and is equivalent — the function receives each group's data slice and returns a nested chart.