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index.js
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index.js
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import fs from 'fs';
import csv from 'csv-parser';
import { createObjectCsvWriter } from 'csv-writer'
import random from 'random';
const REWARDS = 400; // Total number of rewards
const A = 5; // Mapping parameter #1
const B = 1; // Mapping parameter #2
async function readData(path) {
return new Promise((resolve) => {
const data = [];
fs.createReadStream(path).pipe(
csv()
).on('data', (row) => {
data.push(row);
}).on('end', () => {
resolve(data);
});
});
}
function formatData(data) {
let entrants = new Map();
for (let row of data) {
const tickets = Number(row["ticketsBought"]);
if (entrants.has(row["walletId"])) {
entrants.set(row["walletId"], entrants.get(row["walletId"]) + tickets);
} else {
entrants.set(row["walletId"], tickets);
}
}
entrants = Array.from(entrants, ([wallet, tickets]) => ({ wallet, tickets }));
return entrants;
}
function scale(x) {
return A * Math.pow(x, B);
}
function scaleInverse(x) {
return Math.round(Math.pow(x / A, 1 / B));
}
function drawRewards(data, rewards) {
let tickets = 0;
for (let entrant of data) {
tickets += entrant["tickets"];
}
const p = rewards / tickets;
let awarded = 0;
for (let entrant of data) {
const t = entrant["tickets"];
const n = scale(t);
const x = random.binomial(n, p)();
const r = scaleInverse(x);
// console.log(t * p, r);
entrant["rewards"] = r;
entrant["ev"] = t * p;
entrant["delta"] = r - (t * p);
entrant["delta_rel"] = r / (t * p) - 1;
awarded += r;
}
data.sort(entrant => entrant["delta"]);
if (awarded < rewards) {
for (let i = 0; i < rewards - awarded; i++) {
data[i]["rewards"] += 1;
}
} else if (awarded > rewards) {
for (let i = 0; i < awarded - rewards;) {
if (data[data.length - 1 - i]["rewards"] > 0) {
data[data.length - 1 - i]["rewards"] -= 1;
i++;
}
}
}
let awarded2 = 0;
for (let entrant of data) {
awarded2 += entrant["rewards"];
}
console.log(awarded, awarded2);
return data;
}
// Write array of objects to csv file
async function writeData(data, path) {
return new Promise((resolve) => {
const csvWriter = createObjectCsvWriter({
path: path,
header: [
{ id: 'wallet', title: 'Wallet' },
{ id: 'tickets', title: 'Tickets' },
{ id: 'rewards', title: 'Rewards' },
{ id: 'ev', title: 'EV'},
{ id: 'delta', title: 'Delta' },
{ id: 'delta_rel', title: 'Delta rel' }
]
});
csvWriter.writeRecords(data).then(() => {
resolve();
});
});
}
/*
Takes the sample .csv file as an input and returns an array of objects,
where each item corresponds to an unique entrant (walletId) and contains
the information about the number of tickets and rewards won.
Example input: see data.csv
Example output: [
{
wallet: '8bTjRMgkuFKBfMvfCbhbNpMDdZMP5J9iHm4MUULAzW',
tickets: 1,
rewards: 1,
delta: -1
},
{
wallet: '9kvm9DF2J7veAMKEodJtDcArntSrbMkGvKxvpDCB7w6',
tickets: 1,
rewards: 1,
delta: -1
},
{
wallet: '7MKk54ChBTcVpuZ5rLw3y51KqBgGgKzLWzdhU2bLrpV',
tickets: 1,
rewards: 0,
delta: -1
},
...
]
*/
async function main() {
// Reads the .csv file
const data = await readData("data.csv");
// console.log(data);
// Formats the data so that each array item corresponds to an unique entrant
const entrants = formatData(data);
// console.log(entrants);
// Determines the number of rewards that each entrant will receive
const rewards = drawRewards(entrants, REWARDS);
// console.log(rewards);
// Writes the results to a .csv file
await writeData(rewards, "rewards.csv");
}
main();