new template for arrays of objects (collections?)

chapters/arrays/where-for-arrays-of-objects.md

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+---
+layout: recipe
+title: where for arrays of objects
+chapter: Arrays
+---
+## Problem
+
+You want to get an array of objects that match your request for some properties
+
+You have an Array of Objects, such as:
+
+{% highlight coffeescript %}
+cats = [
+  {
+    name: "Bubbles"
+    favoriteFood: "mice"
+    age: 1
+  },
+  {
+    name: "Sparkle"
+    favoriteFood: "tuna"
+  },
+  {
+    name: "flyingCat"
+    favoriteFood: "mice"
+    age: 1
+  }
+]
+{% endhighlight %}
+
+You want to filter with some properties, like cats.where({ age: 1}) or cats.where({ age: 1, favoriteFood: "mice"})
+
+## Solution
+
+You can extend Array like this : 
+
+{% highlight coffeescript %}
+Array::where = (query) ->
+    return [] if typeof query isnt "object"
+    hit = Object.keys(query).length
+    @filter (item) ->
+        match = 0
+        for key, val of query
+            match += 1 if item[key] is val
+        if match is hit then true else false
+
+cats.where age:1
+# => [ { name: 'Bubbles', favoriteFood: 'mice', age: 1 },{ name: 'flyingCat', favoriteFood: 'mice', age: 1 } ]
+
+cats.where age:1, name: "Bubbles"
+# => [ { name: 'Bubbles', favoriteFood: 'mice', age: 1 } ]
+
+cats.where age:1, favoriteFood:"tuna"
+# => []
+{% endhighlight %}
+
+## Discussion
+
+This is an exact match. we could make it more flexible with a matcher function :
+
+{% highlight coffeescript %}
+Array::where = (query, matcher = (a,b) -> a is b) ->
+    return [] if typeof query isnt "object"
+    hit = Object.keys(query).length
+    @filter (item) ->
+        match = 0
+        for key, val of query
+            match += 1 if matcher(item[key], val)
+        if match is hit then true else false
+
+cats.where name:"bubbles"
+# => []
+# it's case sensitive
+
+cats.where name:"bubbles", (a, b) -> "#{ a }".toLowerCase() is "#{ b }".toLowerCase()
+# => [ { name: 'Bubbles', favoriteFood: 'mice', age: 1 } ]
+# now it's case insensitive
+{% endhighlight %}
+
+it's more a method to deal with collection and it could be rename as "find" but popular libraires like underscore or lodash name it "where".