merge-csv-data.js

const arr1 = [
  ['name', 'id', 'age', 'weight'],
  ['Susan', '3', '20', '120'],
  ['John', '1', '21', '150'],
  ['Bob', '2', '23', '90'],
  ['Ben', '4', '20', '100'],
];

const arr2 = [
  ['name', 'id', 'height'],
  ['Bob', '2', '50'],
  ['John', '1', '45'],
  ['Ben', '4', '43'],
  ['Susan', '3', '48'],
];

const arr3 = [
  ['name', 'id', 'parent'],
  ['Bob', '2', 'yes'],
  ['John', '1', 'yes'],
];

function parseCsvArray(array) {
  const [headings, ...rows] = array;

  return rows.map((cols) => {
    const entries = cols.map((col, index) => [headings[index], col]);

    return Object.fromEntries(entries);
  });
}

function mergeById(rows) {
  const ids = new Set(rows.map(({ id }) => id)); // All unique ids

  return [...ids].map((currentId) => {
    const dataForId = rows.filter(({ id }) => id === currentId);

    return dataForId.reduce((acc, row) => ({ ...acc, ...row }));
  });
}

const allData = [
  ...parseCsvArray(arr1),
  ...parseCsvArray(arr2),
  ...parseCsvArray(arr3),
];

console.log(mergeById(allData));