Hierarchy layouts should allow non-root nodes as input?

[ernest-okot]

When a descendant node (i.e depth != 0) is 'partitioned', it's children will be be positioned inaccurately.

Here the 'world' node is 'partitioned'

partition()(world)

Here the 'africa' node is partitioned, because the 'africa' node depth > 0, the layout gets broken

partition()(africa)

[curran]

Would you be able to share a running code example that demonstrates this behavior? Thank you.

[ernest-okot]

sure!

i've pieced together a fiddle https://jsfiddle.net/devacholi/k3m83ofn/3/

const data = [
  {"label": 'World',}, 
  {"label": 'Europe', "parent": 'World'}, 
  {"label": 'Portugal', "parent": 'Europe', "value": 30}, 
  {"label": 'Spain', "parent": 'Europe', "value": 120}, 
  {"label": 'South America', "parent": 'World',"value": 320},
  {"label": 'Africa',"parent": 'World'},
  {"label": 'Uganda', "parent": 'Africa',}, 
  {"parent": 'Uganda',"label": 'Jinja',"value": 20,},
  { "parent": 'Uganda', "label": 'Kampala', "value": 40,},
  { "label": 'Kenya', "parent": 'Africa', "value": 70,}, 
]

const stratify = d3.stratify()
  .id(d => d.label)
  .parentId(d => d.parent);

const layout = d3.partition()

const root = stratify(data)
	.sum(d => d.value)
  .sort((a,b) => a.value - b.value);

// node.depth = 0
const okRectangles = layout(root)
  .descendants()

console.log('expecting 0, got ' +  okRectangles.filter(r => r.y1 > 1).length)
// expecting 0, got 0

// root.children[0].depth = 1
const badRectangles = layout(root.children[0])
  .descendants()

console.log('expecting 0, got ' + badRectangles.filter(r => r.y1 > 1).length)
// expecting 0, got 2

[mbostock]

Per #80 (comment), this is a documented limitation; the hierarchy layouts take a root node as input, not any node. To quote the README:

Before you can compute a hierarchical layout, you need a root node.

And:

node.depth - zero for the root node, and increasing by one for each descendant generation.

You can use node.copy to create a new root from an existing node’s subtree.

My longer-term goal for this module is that the hierarchy layouts no longer mutate the input data (#62). That would make it easier to avoid the call to node.copy before computing the layout. But I don’t think it’s worth fixing this issue in just one of the layouts, when the other layouts have the same problem. It would be reasonable to add some text to the README to clarify this limitation and the recommended workaround in the interim.

[mbostock]

Retitled to generalize this issue.

[ernest-okot]

Thanks for the explanation

Didn't know about node.copy. Not sure if it would be of help if I wanted to maintain the parent relationship of the new root