aggregated_data = Array.from(d3.rollup(raw_data, v => ({
black_alone: d3.sum(v, d=> d.black_alone),
latino_alone: d3.sum(v, d=> d.latino_alone),
total: d3.sum(v, d=> d.total),
geoid: v[0].geoid.slice(0, maxDigit)
}),
d => d.geoid.slice(0, maxDigit)).values())