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

Signature

ChartBuilder.mark(mark) -> ChartBuilder

Parameters

Parameter	Type	Description
mark	Mark | callable	A mark factory result, or a (data) -> ChartBuilder function

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
area	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 select():

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

The mark-as-function pattern

mark() also accepts a function (data) -> ChartBuilder. The function receives each group's data slice and returns a nested chart, letting you build custom glyphs:

chart(seafood).flow(spread(by="lake", dir="x")).mark(
    lambda group: chart(group).flow(stack(by="species", dir="y")).mark(rect(h="count"))
)