chapter02.js

var lyrics = [];

for (var bottles = 99; bottles > 0; bottles--) {
  lyrics.push(bottles + " bottles of beer on the wall");
  lyrics.push(bottles + " bottles of beer");
  lyrics.push("Take one down, pass it around");

  if (bottles > 1) {
    lyrics.push((bottles - 1) + " bottles of beer on the wall.");
  }
  else {
    lyrics.push("No more bottles of beer on the wall!");
  }
}

function lyricSegment(n) {
  return _.chain([])
    .push(n + " bottles of beer on the wall")
    .push(n + " bottles of beer")
    .push("Take one down, pass it around")
    .tap(function(lyrics) {
           if (n > 1)
             lyrics.push((n - 1) + " bottles of beer on the wall.");
           else
             lyrics.push("No more bottles of beer on the wall!");
         })
    .value();
}

function song(start, end, lyricGen) {
  return _.reduce(_.range(start,end,-1),
    function(acc,n) {
      return acc.concat(lyricGen(n));
    }, []);
}

var nums = [1,2,3,4,5];

function doubleAll(array) {
  return _.map(array, function(n) { return n*2 });
}

doubleAll(nums);
//=> [2, 4, 6, 8, 10]

function average(array) {
  var sum = _.reduce(array, function(a, b) { return a+b });
  return sum / _.size(array);
}

average(nums);
//=> 3

/* grab only even numbers in nums */
function onlyEven(array) {
  return _.filter(array, function(n) {
    return (n%2) === 0;
  });
}

onlyEven(nums);
//=> [2, 4]

function allOf(/* funs */) {
  return _.reduceRight(arguments, function(truth, f) {
    return truth && f();
  }, true);
}

function anyOf(/* funs */) {
  return _.reduceRight(arguments, function(truth, f) {
    return truth || f();
  }, false);
}

function complement(pred) {
  return function() {
    return !pred.apply(null, _.toArray(arguments));
  };
}

function cat() {
  var head = _.first(arguments);
  if (existy(head))
    return head.concat.apply(head, _.rest(arguments));
  else
    return [];
}

cat([1,2,3], [4,5], [6,7,8]);
//=> [1, 2, 3, 4, 5, 6, 7, 8]

function construct(head, tail) {
  return cat([head], _.toArray(tail));
}

construct(42, [1,2,3]);
//=> [42, 1, 2, 3]

function mapcat(fun, coll) {
  return cat.apply(null, _.map(coll, fun));
}

function butLast(coll) {
  return _.toArray(coll).slice(0, -1);
}

function interpose (inter, coll) {
  return butLast(mapcat(function(e) {
    return construct(e, [inter]);
  },
  coll));
}

var zombie = {name: "Bub", film: "Day of the Dead"};

_.keys(zombie);
//=> ["name", "film"]

_.values(zombie);
//=> ["Bub", "Day of the Dead"]

var library = [{title: "SICP", isbn: "0262010771", ed: 1},
               {title: "SICP", isbn: "0262510871", ed: 2},
               {title: "Joy of Clojure", isbn: "1935182641", ed: 1}];

_.findWhere(library, {title: "SICP", ed: 2});

//=> {title: "SICP", isbn: "0262510871", ed: 2}

function project(table, keys) {
  return _.map(table, function(obj) {
    return _.pick.apply(null, construct(obj, keys));
  });
};

function rename(obj, newNames) {
  return _.reduce(newNames, function(o, nu, old) {
    if (_.has(obj, old)) {
      o[nu] = obj[old];
      return o;
    }
    else
      return o;
  },
  _.omit.apply(null, construct(obj, _.keys(newNames))));
};

function as(table, newNames) {
  return _.map(table, function(obj) {
    return rename(obj, newNames);
  });
};

function restrict(table, pred) {
  return _.reduce(table, function(newTable, obj) {
    if (truthy(pred(obj)))
      return newTable;
    else
      return _.without(newTable, obj);
  }, table);
};