d3.js v4: How to access parent group's datum index?

Question

The description of the selection.data function includes an example with multiple groups (link) where a two-dimensional array is turned into an HTML table.

Answer 1

My workaround is somewhat similar to Dinesh Rajan's, assuming the parent index is needed for attribute someAttr of g.nestedElt:

v3:

svg.selectAll(".someClass")
    .data(nestedData)
  .enter()
  .append("g")
    .attr("class", "someClass")
  .selectAll(".nestedElt")
    .data(Object)
  .enter()
  .append("g")
    .attr("class", "nestedElt")
    .attr("someAttr", function(d, i, j) {

    });

v4:

svg.selectAll(".someClass")
    .data(nestedData)
  .enter()
  .append("g")
    .attr("class", "someClass")
    .attr("data-index", function(d, i) { return i; }) // make parent index available from DOM
  .selectAll(".nestedElt")
    .data(Object)
  .enter()
  .append("g")
    .attr("class", "nestedElt")
    .attr("someAttr", function(d, i) {
      var j = +this.parentNode.getAttribute("data-index");
    });