EJ: C5 P2 created by oliverjam - https://repl.it/ES00/2

EJ: C5 P2.js

function average(array) {
  function plus(a, b) { return a + b; }
  return array.reduce(plus) / array.length;
}

var byName = {};
ancestry.forEach(function(person) {
  byName[person.name] = person;
});

function avgAgeDiff(data) {
  return data.filter(entry => byName[entry.mother] !== null && byName[entry.mother] !== undefined)
  					   .map(entry => entry.born - byName[entry.mother].born);
}

console.log(average(avgAgeDiff(ancestry)));
// Get an array of age differences (map?)
// Filter out null answers
// Average the array

// → 31.2