Add nest.count or nest.visit?

[mbostock]

Copied from d3/d3-array#10:

Related d3/d3#1091, it might be nice if there were an easy way to count the number of elements matched at each level of the hierarchy. Yes, things like the cluster layout do that for you already, but it’d be nice to do that with a simple nest operator, too.

This feels slightly related to the nest.rollup method, too. Like, instead of replacing the set of nested values with the return value of the rollup function, I just want to decorate the object (say by assigning a count value). But another big difference is that rollup only operates on arrays of siblings, and nest.count should be a recursive operation on the entire tree.

So… it’s almost like you want tree visit methods on the returned nest object. Which makes me wonder if there should be a nest.tree method instead of nest.map, and then have some useful methods on the returned tree instance.

[mbostock]

The current solution is to pass the result of nest.entries to d3.hierarchy.