chalu

const isFemale = match('gender', is('female'));
const isYoungAdult = match('age', isOrOver(18));
const canPlayNightOwl = match('age', isUnder(60));
const ageIsSpecialNumber = match('age', isMultipleOf(4));

const getSpecialFemaleDevs = chain(
  isFemale,
  isYoungAdult,
  canPlayNightOwl,
  ageIsSpecialNumber

chalu

const is = (target) => (value) => value === target;
const isOver = (target) => (value) => value > target;
const isOrOver = (target) => (value) => value >= target;

// match devs over 24 years old
const olderThan24 = match('age', isOver(24));
const over24s = olderThan24(data);

// match devs at, or over 35 years old
const aged35OrOlder = match('age', isOrOver(35));

chalu

const isOver24 = (value) => value > 24;
const getOver24s = match('age', isOver24);
const over24s = getOver24s(data);

chalu

const match = (field, delegate) => {
  return (data = []) => {
    return data.filter(entry => delegate(entry[field]));
  }
};

const isMale = (value) => value === 'male';
const isFemale = (value) => value === 'female';

chalu

const getFemales = match('gender', isFemale);
const femaleDevs = getFemales(data);

chalu

const sumAges = compute(sumOf, 'age');
const sumOfAge = sumAges(data);

const avgAge = compute(averageOf, 'age');
const averageAge = avgAge(data);

console.log(`... while total age of African developers was ${sumOfAge}, the average age was ${averageAge}`);

chalu

const sumOf = (data = [], field) => {
  return data.reduce((sum, entry) => {
    return sum += entry[field] || 0;
  }, 0);
};

const averageOf = (data = [], field) => {
  return data.reduce((sum = 0, entry, index) => {
    const sum += (entry[field] || 0);

chalu

const compute = (delegate, field) => {
  return (data) => delegate(data, field);
};

chalu

const avgAge = compute(averageOf, 'age');
const avgOfAges = avgAge(data);

chalu

const sumAges = compute(sumOf, 'age');
const sumOfAge = sumAges(data);