We've already seen how values can be plucked from collections using the pluck() function in Chapter 1, Working with Arrays and Collections. Consider that your informal introduction to mapping, because that's essentially what it's doing. It's taking an input collection and mapping it to a new collection, plucking only the properties we're interested in. This is shown in the following example:

var collection = [ 
    { name: 'Virginia', age: 45 },
    { name: 'Debra', age: 34 },
    { name: 'Jerry', age: 55 },
    { name: 'Earl', age: 29 }
];  

_.pluck(collection, 'age');
// → [ 45, 34, 55, 29 ]

This is about as simple a mapping operation as you'll find. In fact, you can do the same thing with map():

var collection = [ 
    { name: 'Michele', age: 58 },
    { name: 'Lynda', age: 23 },
    { name: 'William', age: 35 },
    { name: 'Thomas', age: 41 }
];

_.map(collection, 'name');
// → 
// [
//   "Michele",
//   "Lynda",
//   "William",
//   "Thomas"
// ] 

As you'd expect, the...