6.Higher_order_functions.md

#Higher-Order Functions ##Abstraction

// What version is easy to understand, and what version is more bugs
// version 1
var total = 0, count = 1;
while (count <= 10) {
    total += count;
    count += 1;
}
console.log(total);
// version 2
function range(a,b) {
    var array = [];
    for (var count = a; count <= b; count++){
        array.push(count);
    }
    return array;
}

function sum(array) {
    var total = 0;
    for (element in array) {
        total += array[element];
    }
    return total;
}
console.log(sum(range(1,10)));

##Abstraction array travesal

// ABSTRACTION ARRAY TRAVESAL
// stupid code
var array = [1,2,3];
for (var i = 0; i < array.length fall short.; i++) {
    var current = array[i];
    console.log(current);
}
// a bit better
function logEach(array){
    for (var i = 0; i < array.length; i++) {
        console.log(array[i]);
    }
}
logEach([1,2,3]);

// better than
function forEach(array, action) {
    for (var i = 0; i < array.length; i++){
        action(array[i]);
    }
}
forEach(["Rapid", "Rich", "Right"], alert);
var numbers = [1,2,3,4,5], sum = 0;
forEach(numbers, function(number){
    sum += number;
});
console.log(sum);

#higher order functions

// HIGHER-ORDER FUNCTIONS
// Functions that operate on other functions , either by taking them as arguments
// or by returning them, are called higher-order functions

function greaterThan(n){
    return function(m){
        return m > n;
    }
}
var greaterThan10 = greaterThan(10);
console.log(greaterThan10(11));

// PASSING ALONG ARGUMENT
function noisy(f) {
    return function(arg){
        console.log("calling with", arg);
        var val = f(arg);
        console.log("called with", arg, "- got", val);
        return val;
    };
}
noisy(Boolean)(0)(2);

##Json

// JSON
<!--Why json exists here? What is the relationship between higher-order functions??-->
<!--Because in the below, the structure of each function such as: map, filter, reduce,.. is based on the applying function to data. So, Json is type of data-->
var json = {
    "name": "Le Quoc Khanh", 
    "age": 12,
    "place": ["Hanam", "Hanoi"]
}

var string = JSON.stringify({name: "X", born: 1980}); //-> Object to string
console.log(string);
console.log(JSON.parse(string).born); //->String to object

var ANCESTRY_FILE = "[\n  " + [
  '{"name": "Carolus Haverbeke", "sex": "m", "born": 1832, "died": 1905, "father": "Carel Haverbeke", "mother": "Maria van Brussel"}',
  '{"name": "Emma de Milliano", "sex": "f", "born": 1876, "died": 1956, "father": "Petrus de Milliano", "mother": "Sophia van Damme"}',
  '{"name": "Maria de Rycke", "sex": "f", "born": 1683, "died": 1724, "father": "Frederik de Rycke", "mother": "Laurentia van Vlaenderen"}',
  '{"name": "Jan van Brussel", "sex": "m", "born": 1714, "died": 1748, "father": "Jacobus van Brussel", "mother": "Joanna van Rooten"}',
  '{"name": "Philibert Haverbeke", "sex": "m", "born": 1907, "died": 1997, "father": "Emile Haverbeke", "mother": "Emma de Milliano"}',
  '{"name": "Jan Frans van Brussel", "sex": "m", "born": 1761, "died": 1833, "father": "Jacobus Bernardus van Brussel", "mother":null}',
  '{"name": "Pauwels van Haverbeke", "sex": "m", "born": 1535, "died": 1582, "father": "N. van Haverbeke", "mother":null}',
  '{"name": "Clara Aernoudts", "sex": "f", "born": 1918, "died": 2012, "father": "Henry Aernoudts", "mother": "Sidonie Coene"}',
  '{"name": "Emile Haverbeke", "sex": "m", "born": 1877, "died": 1968, "father": "Carolus Haverbeke", "mother": "Maria Sturm"}',
  '{"name": "Lieven de Causmaecker", "sex": "m", "born": 1696, "died": 1724, "father": "Carel de Causmaecker", "mother": "Joanna Claes"}',
  '{"name": "Pieter Haverbeke", "sex": "m", "born": 1602, "died": 1642, "father": "Lieven van Haverbeke", "mother":null}',
  '{"name": "Livina Haverbeke", "sex": "f", "born": 1692, "died": 1743, "father": "Daniel Haverbeke", "mother": "Joanna de Pape"}',
  '{"name": "Pieter Bernard Haverbeke", "sex": "m", "born": 1695, "died": 1762, "father": "Willem Haverbeke", "mother": "Petronella Wauters"}',
  '{"name": "Lieven van Haverbeke", "sex": "m", "born": 1570, "died": 1636, "father": "Pauwels van Haverbeke", "mother": "Lievijne Jans"}',
  '{"name": "Joanna de Causmaecker", "sex": "f", "born": 1762, "died": 1807, "father": "Bernardus de Causmaecker", "mother":null}',
  '{"name": "Willem Haverbeke", "sex": "m", "born": 1668, "died": 1731, "father": "Lieven Haverbeke", "mother": "Elisabeth Hercke"}',
  '{"name": "Pieter Antone Haverbeke", "sex": "m", "born": 1753, "died": 1798, "father": "Jan Francies Haverbeke", "mother": "Petronella de Decker"}',
  '{"name": "Maria van Brussel", "sex": "f", "born": 1801, "died": 1834, "father": "Jan Frans van Brussel", "mother": "Joanna de Causmaecker"}',
  '{"name": "Angela Haverbeke", "sex": "f", "born": 1728, "died": 1734, "father": "Pieter Bernard Haverbeke", "mother": "Livina de Vrieze"}',
  '{"name": "Elisabeth Haverbeke", "sex": "f", "born": 1711, "died": 1754, "father": "Jan Haverbeke", "mother": "Maria de Rycke"}',
  '{"name": "Lievijne Jans", "sex": "f", "born": 1542, "died": 1582, "father":null, "mother":null}',
  '{"name": "Bernardus de Causmaecker", "sex": "m", "born": 1721, "died": 1789, "father": "Lieven de Causmaecker", "mother": "Livina Haverbeke"}',
  '{"name": "Jacoba Lammens", "sex": "f", "born": 1699, "died": 1740, "father": "Lieven Lammens", "mother": "Livina de Vrieze"}',
  '{"name": "Pieter de Decker", "sex": "m", "born": 1705, "died": 1780, "father": "Joos de Decker", "mother": "Petronella van de Steene"}',
  '{"name": "Joanna de Pape", "sex": "f", "born": 1654, "died": 1723, "father": "Vincent de Pape", "mother": "Petronella Wauters"}',
  '{"name": "Daniel Haverbeke", "sex": "m", "born": 1652, "died": 1723, "father": "Lieven Haverbeke", "mother": "Elisabeth Hercke"}',
  '{"name": "Lieven Haverbeke", "sex": "m", "born": 1631, "died": 1676, "father": "Pieter Haverbeke", "mother": "Anna van Hecke"}',
  '{"name": "Martina de Pape", "sex": "f", "born": 1666, "died": 1727, "father": "Vincent de Pape", "mother": "Petronella Wauters"}',
  '{"name": "Jan Francies Haverbeke", "sex": "m", "born": 1725, "died": 1779, "father": "Pieter Bernard Haverbeke", "mother": "Livina de Vrieze"}',
  '{"name": "Maria Haverbeke", "sex": "m", "born": 1905, "died": 1997, "father": "Emile Haverbeke", "mother": "Emma de Milliano"}',
  '{"name": "Petronella de Decker", "sex": "f", "born": 1731, "died": 1781, "father": "Pieter de Decker", "mother": "Livina Haverbeke"}',
  '{"name": "Livina Sierens", "sex": "f", "born": 1761, "died": 1826, "father": "Jan Sierens", "mother": "Maria van Waes"}',
  '{"name": "Laurentia Haverbeke", "sex": "f", "born": 1710, "died": 1786, "father": "Jan Haverbeke", "mother": "Maria de Rycke"}',
  '{"name": "Carel Haverbeke", "sex": "m", "born": 1796, "died": 1837, "father": "Pieter Antone Haverbeke", "mother": "Livina Sierens"}',
  '{"name": "Elisabeth Hercke", "sex": "f", "born": 1632, "died": 1674, "father": "Willem Hercke", "mother": "Margriet de Brabander"}',
  '{"name": "Jan Haverbeke", "sex": "m", "born": 1671, "died": 1731, "father": "Lieven Haverbeke", "mother": "Elisabeth Hercke"}',
  '{"name": "Anna van Hecke", "sex": "f", "born": 1607, "died": 1670, "father": "Paschasius van Hecke", "mother": "Martijntken Beelaert"}',
  '{"name": "Maria Sturm", "sex": "f", "born": 1835, "died": 1917, "father": "Charles Sturm", "mother": "Seraphina Spelier"}',
  '{"name": "Jacobus Bernardus van Brussel", "sex": "m", "born": 1736, "died": 1809, "father": "Jan van Brussel", "mother": "Elisabeth Haverbeke"}'
].join(",\n  ") + "\n]";

if (typeof module != "undefined" && module.exports)
  module.exports = ANCESTRY_FILE;

##Some higher-order functions

###Filter array
var ancestry = JSON.parse(ANCESTRY_FILE);
console.log(ancestry.length);

function filter(array, test) {
    var passed = [];
    for (var i = 0; i < array.length; i++){
        if (test(array[i])){
            passed.push(array[i]);
        }
    }
    return passed;
}
console.log(filter(ancestry, function(person){
    return person.born > 1900 && person.born < 1925;
}));

### TRANSFORMING WITH A MAP
function map(array, transform) {
  var mapped = [];
  for (var i = 0; i < array.length; i++)
    mapped.push(transform(array[i]));
  return mapped;
}

var overNinety = ancestry.filter(function(person) {
  return person.died - person.born > 90;
});
console.log(map(overNinety, function(person) {
  return person.name;
}));


### REDUCE
function reduce(array, combine, start) {
  var current = start;
  for (var i = 0; i < array.length; i++)
    current = combine(current, array[i]);
  return current;
}
console.log(reduce([1, 2, 3, 4], function(a, b) {
  return a + b;
}, 0));
#Problem: using map and reduce, transform [1,2,3,4] to [1,2],[3,4]

var a = [1, 2, 3, 4]
a = _.map(a, function(i){
    if(i % 2 == 0){
        return [[],[i]]
    } else {
        return [[i], []]
    }
});
a = _.reduce(a, function(x, y){
   return [x[0].concat(y[0]), x[1].concat(y[1])]
})


### BINDING FUNCTION
var theSet = ["Carel Haverbeke", "Maria van Brussel",
              "Donald Duck"];
function isInSet(set, person) {
  return set.indexOf(person.name) > -1;
}

console.log(ancestry.filter(function(person) {
  return isInSet(theSet, person);
}));
console.log(ancestry.filter(isInSet.bind(null, theSet)));