Solution to eloquentjavascript exercise second 2nd edition (Chapter 5) eloquent javascript

gistfile1.js

// Solution to eloquentjavascript exercise second 2nd edition
// Chapter 5
// http://eloquentjavascript.net/2nd_edition/preview/05_higher_order.html

// Mother-child age difference
function average(array) {
  function plus(a, b) { return a + b; }
  return array.reduce(plus) / array.length;
}

var byName = {};
console.log(typeof ancestry)
ancestry.forEach(function(person) {
  byName[person.name] = person;
});
// Your code here.
var hasKnownMother = function(person) {
    return person.mother in byName;
};

function getAgeDiff(person) {
    return person.born - byName[person.mother].born
}

console.log(average(ancestry.filter(hasKnownMother).map(getAgeDiff)));
// → 31.2
// ---------------------------------------
// Flattening
console.log(arrays.reduce(function(res, nextItem) {
	return res.concat(nextItem);} ));
	
// ---------------------------------------
// Historical life expectancy
var perCentury = {};
ancestry.forEach(function(person) {
    var cent = String(Math.ceil(person.died/100));
    if (!(cent in perCentury)) {
        perCentury[cent] = [];
    }
    perCentury[cent].push(person.died - person.born);
});

for (cent in perCentury) {
    console.log(cent, '->', average(perCentury[cent]));
}
// bonus
function groupBy(a, classifyFunc) {
    return a.map(classifyFunc).reduce(function (curr, item, idx) {
        if (!(item in curr)) {
            curr[item] = [a[idx]];
        } else {
            curr[item].push(a[idx]);
        }
        return curr;
    }, {});
}

function byDeathCent(person) {
    return String(Math.ceil(person.died/100));
}

var groups = groupBy(ancestry, byDeathCent);
for (cent in groups) {
    var avg = average(groups[cent].map(function (person) {
        return person.died - person.born;
    }));
    console.log(cent, '->', avg);
}

// ---------------------------------------
// Every and then some
function every(a, predicate) {
    for (var i=0; i< a.length; ++i) {
        if (!(predicate(a[i]))) {
            return false
        }
    }
    return true;
}

function some(a, predicate) {
    for (var i=0; i< a.length; ++i) {
        if (predicate(a[i])) {
            return true;
        }
    }
    return false;
}

Very useful! Thanks a lot!

Very useful!