function getRadialDomain(data) {
  return data.reduce((res, row) => Math.max(row.radius, res), 0);
}
Find the max radius value from the nodes to be rendered after they have been
transformed into an array
@param {Array} data - the tree data after it has been broken into a iterable
it is an array of objects!
@returns {number} the maximum value in coordinates for the radial variable