Finds the mark groups that make up a Plot.tree or Plot.cluster.
Neither is a mark. Both are three of them — a link for the edges, a dot
for the nodes, and a text for the names, which Plot draws as two text
marks because leaf labels and internal-node labels sit on opposite sides of
their dot. Read individually the hierarchy disappears: the dots become a
scatter whose coordinates are where the layout algorithm put each node, and
the links, which are the only place the structure lives, produce no layer at
all (#1168).
What identifies it is not the arrangement but a fact in the markup. Plot
gives every tree node a <title> holding its full path from the root,
and — measured across delimiters — always joined with / whatever the
caller's own delimiter was:
So the test is whether the node titles form a rooted hierarchy: every one
begins with /, and every one's parent prefix is either empty or another
title. A labelled scatter whose labels happen to look like paths fails that
as soon as one of its parents is missing, and a link mark on its own keeps
the span reading #1094 gave it.
One tree per plot. Two of them share a pair of scales and draw on top of one
another, so the chart is not one anybody makes; the first is read and the
second is left as it was rather than the two being merged into a hierarchy
neither draws.
Finds the mark groups that make up a
Plot.treeorPlot.cluster.Neither is a mark. Both are three of them — a
linkfor the edges, adotfor the nodes, and atextfor the names, which Plot draws as two text marks because leaf labels and internal-node labels sit on opposite sides of their dot. Read individually the hierarchy disappears: the dots become a scatter whose coordinates are where the layout algorithm put each node, and the links, which are the only place the structure lives, produce no layer at all (#1168).What identifies it is not the arrangement but a fact in the markup. Plot gives every tree node a
<title>holding its full path from the root, and — measured across delimiters — always joined with/whatever the caller's owndelimiterwas:So the test is whether the node titles form a rooted hierarchy: every one begins with
/, and every one's parent prefix is either empty or another title. A labelled scatter whose labels happen to look like paths fails that as soon as one of its parents is missing, and alinkmark on its own keeps the span reading #1094 gave it.One tree per plot. Two of them share a pair of scales and draw on top of one another, so the chart is not one anybody makes; the first is read and the second is left as it was rather than the two being merged into a hierarchy neither draws.