underscore hw

$$ = λ = function(body) {
    return function() {
        var a = arguments;
        var x = arguments[0];
        var y = arguments[1];
        var z = arguments[2];
        return eval("("+body+")");
    };
};

// 1 Write a method that from a given array of students finds all students whose first name is before its last name alphabetically. Print the students in descending order by full name. Use Underscore.js

var protoStudent = {
    fullName: function() { return this.firstName + " " + this.lastName; }
};

var makeStudent = function(fname, lname, age, marks) {
    return _.extend(Object.create(protoStudent),
        { firstName: fname, lastName: lname, age: age, marks: marks });
};

var makeStudents = function() {
    return _.map(arguments, λ('makeStudent.apply(null,x)'));
};

var students = makeStudents(
    ['Joro','Peshev',25,[4,4.5,6,2]],
    ['Aaaaa', 'Zzzzz', 100,[]],
    ['Minka', 'Tosheva', 22,[2.5,6.0,4.0]],
    ['Pesho','Jorev', 30,[6.0,5.5]]
);

var task1 = function() {
    var ourStudents = _.chain(students)
        .filter(λ('x.firstName < x.lastName'))
        .sortBy(λ('x.fullName()'))
        .values()
        .reverse();

    _(ourStudents).each(λ('console.log(x.fullName())'));
};

// 2 Write function that finds the first name and last name of all students with age between 18 and 24. Use Underscore.js

var task2 = function() {
    return _.chain(students)
        .filter(λ('18 <= x.age && x.age <= 24'))
        .map(λ('x.fullName()'))
        .value();
};

// 3 Write a function that by a given array of students finds the student with highest marks

var average = function(arr) {
    return _.reduce(arr, λ('x+y'), 0) / arr.length;
};

var task3 = function() {
    return _(students)
        .max(λ('average(x.marks)'));
};

// 4 Write a function that by a given array of animals, groups them by species and sorts them by number of legs

var makeAnimals = function() {
    return _(arguments)
        .map(λ('{ name: x[0], species: x[1], legs: x[2] }'));
};

var animals = makeAnimals(
    ["ginger", "rabbit", 4],
    ["winner", "dog", 4],
    ["chuck", "chicken", 2],
    ["chernobyl", "chicken", 6],
    ["harold", "spider", 8],
    ["smith", "pig", 4],
    ["samuel", "octopus", 8],
    ["horace the survivor", "pig", 3]
);

var task4 = function() {
    var groups = _(animals).groupBy(λ('x.species'));

    // sort animals in each group?
    // var sortedGroups = _(groups).map(λ('_(x).sortBy(λ("x.legs"))'));

    // sort all groups?
    var sortedGroups = _(groups).sortBy(λ('x[0].legs'));

    return sortedGroups;
};

// 5 By a given array of animals, find the total number of legs
// Each animal can have 2, 4, 6, 8 or 100 legs

var task5 = function() {
    return _.chain(animals)
        .pluck('legs')
        .reduce(λ('x+y'), 0)
        .value();
};

// 6 By a given collection of books, find the most popular author (the author with the biggest number of books)

var books = _.map(
    [["Stephen King", "The Dark Tower"],
     ["George Orwell", "Animal Farm"],
     ["William Shakespeare", "Much Ado About Nothing"],
     ["George Orwell", "Homage to Catalonia"],
     ["Robert Heinlein", "Starship Troopers"]],
    λ('{author: x[0], title: x[1]}'));

var task6 = function() {
    return _.chain(books)
        .groupBy(λ('x.author'))
        .max(λ('x.length'))
        .value()[0].author;
};

// 7 By an array of people find the most common first and last name. Use underscore.

var people = makeStudents(
    ['Joro','Peshev'],
    ['Minka', 'Tosheva'],
    ['Pesho','Jorev'],
    ['Joro','Goshev'],
    ['Joro', 'Mishev'],
    ['Pesho','Goshev'],
    ['Minkia','Gosheva'],
    ['Pesho','Peshev'],
    ['Gosho','Mishev'],
    ['Joro','Mishev']
);

var task7 = function() {
    var firstName =
        _.chain(people)
            .groupBy(λ('x.firstName'))
            .max(λ('x.length'))
            .value()[0].firstName;

    var lastName =
        _.chain(people)
            .groupBy(λ('x.lastName'))
            .max(λ('x.length'))
            .value()[0].lastName;

    return [firstName, lastName];
};