compute time ever lived in human history

population.mjs

import { writeFileSync } from "node:fs"

// data from https://en.wikipedia.org/wiki/Estimates_of_historical_world_population PRB column
// and https://www.prb.org/articles/how-many-people-have-ever-lived-on-earth
const data = `
-190000	0
-50000	2M
-8000	5M
0	300M
1200	450M
1650	500M
1750	795M
1850	1265M
1900	1656M
1950	2499M
2000	6149M
2010	6986M
2022	7963M
-7000	7M
-6000	14M
-5000	27M
-4000	50M
-3000	100M
-1000	100M
-500	150M
-200	227M
500	280M
1000	400M
1100	450M
1200	500M
1300	500M
1400	500M
1500	600M
1600	600M
1700	660M
1800	1000M
1850	1265M
1900	1656M
1925	2000M
`

const rows = []

data.split(/\n/).forEach(l => {
    let [yr, pop] = l.split(/\s+/)
    yr = parseInt(yr)
    pop = parseInt(pop)
    if (isNaN(yr)) return
    rows.push([yr, pop])
})

rows.sort((a, b) => a[0] - b[0])
let total = 0
for (let i = 1; i < rows.length; ++i) {
    const [y0, p0] = rows[i - 1]
    const [yr, pop] = rows[i]
    const len = yr - y0
    const popavg = (pop + p0) / 2
    const yrslived = Math.round((len * popavg) / 1000)
    total += yrslived
    rows[i].push(len, popavg, yrslived, total)
}
for (let i = 1; i < rows.length; ++i) {
    rows[i].push(
        Math.round((10000 * rows[i][rows[i].length - 1]) / total) / 100
    )
}

rows.unshift([
    "year",
    "population (M)",
    "time",
    "pop.avg (M)",
    "years lived (B)",
    "total years lived (B)",
    "% years lived",
])

writeFileSync("pop.csv", rows.map(r => r.join(",")).join("\n"))