Merge pull request coffeescript-cookbook#21 from joaomoreno/master

Add "Reducing Arrays" recipe

Author: peterhellberg

chapters/arrays/reducing-arrays.textile

@@ -0,0 +1,43 @@
+---
+layout: recipe
+title: Reducing Arrays
+chapter: Arrays
+---
+
+h2. Problem
+
+You have an array of objects and want to reduce them to a value, similar to Ruby's <code>reduce()</code> and <code>reduceRight()</code>.
+
+h2. Solution
+
+You can simply use Array's <code>reduce()</code> and <code>reduceRight()</code> methods along with an anonoymous function, keeping the code clean and readable. The reduction may be something simple such as using the <code>+</code> operator with numbers or strings.
+
+{% highlight coffeescript %}
+[1,2,3,4].reduce (x,y) -> x + y
+# => 10
+{% endhighlight %}
+
+{% highlight coffeescript %}
+["words", "of", "bunch", "A"].reduceRight (x, y) -> x + " " + y
+# => 'A bunch of words'
+{% endhighlight %}
+
+Or it may be something more complex such as aggregating elements from a list into a combined object.
+
+{% highlight coffeescript %}
+people =
+    { name: '', age: 10 }
+    { name: '', age: 16 }
+    { name: '', age: 17 }
+
+people.reduce (x, y) ->
+    x[y.name]= y.age
+    x
+, {}
+# => { alec: 10, bert: 16, chad: 17 }
+{% endhighlight %}
+
+h2. Discussion
+
+Javascript introduced <code>reduce</code> and <code>reduceRight</code> in version 1.8. Coffeescript provides a natural and simple way to express anonymous functions. Both go together cleanly in the problem of merging a collection's items into a combined result.
+

wanted-recipes.textile

@@ -26,12 +26,6 @@ h2. Strings
 
 h2. Arrays
 
-* Reducing arrays to values (ruby inject) with reduce # [1..10].reduce (a,b) -> a+b # 55
-* Reducing arrays in reverse order # JS reduceRight 
-{% highlight coffeescript %}
-["example", "contrived ", "pretty ", "a ", "is ", "here "].reduceRight (x,y) -> x+y
-# => 'here is a pretty contrived example'
-{% endhighlight %}
 * Testing every element in an array
 {% highlight coffeescript %}
 evens = (x for x in [0..10] by 2)