Added arrays/list-comprehensions and arrays/mapping-arrays

Author: David Brady

chapters/arrays/list-comprehensions.textile

@@ -0,0 +1,30 @@
+---
+layout: recipe
+title: List Comprehensions
+chapter: Arrays
+---
+
+h2. Problem
+
+You have an array of objects and want to map them to another array, similar to Python's list comprehensions.
+
+h2. Solution
+
+Use a list comprehension, but don't forget about <a href="/chapters/arrays/mapping-arrays">mapping arrays</a>.
+
+{% highlight coffeescript %}
+electric_mayhem = [ { name: "Doctor Teeth", instrument: "piano" },
+                    { name: "Janice", instrument: "lead guitar" },
+                    { name: "Sgt. Floyd Pepper", instrument: "bass" },
+                    { name: "Zoot", instrument: "sax" },
+                    { name: "Lips", instrument: "trumpet" },
+                    { name: "Animal", instrument: "drums" } ]
+
+names = (muppet.name for muppet in electric_mayhem)
+# => [ 'Doctor Teeth', 'Janice', 'Sgt. Floyd Pepper', 'Zoot', 'Lips', 'Animal' ]
+{% endhighlight %}
+
+h2. Discussion
+
+Because CoffeeScript directly support list comprehensions, they work pretty much as advertised wherever you would use one in Python. For simple mappings, list comprehensions are much more readable. For complicated transformations or for chained mappings, <a href="/chapters/arrays/mapping-arrays">mapping arrays</a> might be more elegant.
+

chapters/arrays/mapping-arrays.textile

@@ -0,0 +1,32 @@
+---
+layout: recipe
+title: Mapping Arrays
+chapter: Arrays
+---
+
+h2. Problem
+
+You have an array of objects and want to map them to another array, similar to Ruby's map.
+
+h2. Solution
+
+Use map() with an anonymous function, but don't forget about <a href="/chapters/arrays/list-comprehensions">list comprehensions</a>.
+
+{% highlight coffeescript %}
+electric_mayhem = [ { name: "Doctor Teeth", instrument: "piano" },
+                    { name: "Janice", instrument: "lead guitar" },
+                    { name: "Sgt. Floyd Pepper", instrument: "bass" },
+                    { name: "Zoot", instrument: "sax" },
+                    { name: "Lips", instrument: "trumpet" },
+                    { name: "Animal", instrument: "drums" } ]
+
+names = electric_mayhem.map (muppet) -> muppet.name
+# => [ 'Doctor Teeth', 'Janice', 'Sgt. Floyd Pepper', 'Zoot', 'Lips', 'Animal' ]
+{% endhighlight %}
+
+h2. Discussion
+
+Because CoffeeScript has clean support for anonymous functions, mapping an array in CoffeeScript is nearly as easy as it is in Ruby.
+
+Maps are are good way to handle complicated transforms and chained mappings in CoffeeScript. If your transformation is as simple as the one above, however, it may read more cleanly as a <a href="/chapters/arrays/list-comprehensions">list comprehension</a>.
+