selection.each()

selection.each(function)

Invokes the specified function for each selected element, passing in passed the current datum (d), the current index (i), and the current group (nodes), with this of the current DOM element. This method can be used to invoke arbitrary code for each selected element, and is useful for creating a context to access parent and child data simultaneously, such as:

parent.each(function(p, j) {
  d3.select(this)
    .selectAll(".child")
      .text(function(d, i) { return "child " + d.name + " of " + p.name; });
});

See Sized Donut Multiples for an example.