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 solution was to embed this information in the data provided to d3js

data = [[1,2,3],[4,5,6],[7,8,9]]
flattened_data = data.reduce((acc, v, i) => {
    v.forEach((d, j) => {
      data_item = { i, j, d };
      acc.push(data_item);
    });
    return acc;
  }, []);

Then you can access i, j and d from the data arg of the function

td.text(function(d) {
  // Can access i, j and original data here
  return "Row: " + d.j;
});