dataWithConstituencies = ({
name: (`Questions in ${year.year}`),
children:
Array.from(
d3.rollup(filtered, v => v.length, d => d.party, d => d.constituency, d => d.department, d => d.heading),
([name, children]) => ({name, children: Array.from(children, ([name, children]) => ({name, children: Array.from(children, ([name, children]) => ({name, children: Array.from(children, ([name, value]) => ({name, value})
)}) )}))})) })
;