function each(array, f) {
  for (var i = 0; i < array.length; i++) {
    f(array[i]);
  }
}

function map(array, f) {
  var acc = [];
  each(array, function(element) {
    acc.push(f(element));
  });
  return acc;
}

function reduce(array, f, start) {
  var acc = start;
  each(array, function(element) {
    acc = f(acc, element);
  });
  return acc;
}

//  function product(numbers) {
//   return reduce(numbers, function(acc, number) {
//     return acc * number;
//   }, 1);
// }

// console.log(product([1, 2, 3, 4]));

// var people = [
//   {name: {first: "Alyssa", middle: "P.", last: "Hacker"}, age: 26},
//   {name: {first: "Ben", last: "Bitdiddle"}, age: 34},
//   {name: {first: "Eva", middle: "Lu", last: "Ator"}, age: 40},
//   {name: {first: "Lem", middle: "E.", last: "Tweakit"}, age: 45},
//   {name: {first: "Louis", last: "Reasoner"}, age: 21}
// ];

// function averageAge(people) {
//   var ages = map(people, function(person) {
//     return person.age;
//   });
//   console.log(ages);
//   return reduce(ages, function(acc, age) {
//     return acc += age;
//   }, 0) / ages.length;
// }

// console.log(averageAge(people));

// function range(start, end) {
//   var acc = [];
//   for (var i = start; i < end; i++) {
//     acc.push(i);
//   }
//   return acc;
// }
// console.log(range(1, 5));
// function factorial(n) {
//   return reduce(range(1, n + 1), function(acc, element) {
//     return acc *= element;
//   }, 1);
// }

// console.log(factorial(4));

// var arr = [1, 2, 3]
// function sumBy(numbers, f) {
//   return reduce(numbers, function(sum, number) {
//     return sum += f(number);
//   }, 0);
//   return sum;
// }

// function square(x) {
//   return x * x;
// }

// function cube(x) {
//   return x * x * x;
// }

//sumBy(arr, square); // => 30
  //Note: you will have to create a function "square" that returns the square of an input number.
//sumBy(arr, cube); // => 100
  //Note: you will have to create a function "cube" that returns the cube of an input number.


// function max(numbers) {
//   var max = numbers[0];
//   each(numbers, function(number) {
//     if (number > max) {
//       max = number;
//     }
//   });
//   return max;
// }

// function max(numbers) {
//   return reduce(numbers, function(max, number) {
//     console.log(number, max);
//     if(number > max) {
//       return max = number;
//     }
//   }, numbers[0]);
// }
// console.log(max([1, 2, 3, 4, 5]));