is sorted

lib/collection_functions.js

@@ -18,6 +18,7 @@ CollectionFunctions = (function(){
     append:function(array, item){ array.push(item) },
     isCollection:function(thing){ return typeof thing.length != "undefined" },
     size:function(array){ return array.length },
+    // sort:function(array){ [].concat(array).sort() },
     concat:function(){
       var firstArray = arguments[0]
       var otherArrays = []
@@ -36,7 +37,7 @@ CollectionFunctions = (function(){
       }
 
       var featureNames = ["iterator", "nothing", "equals", "newCollection", 
-                          "append", "isCollection", "size", "concat"]
+                          "append", "isCollection", "size", "concat", "comparator"]
       for (var i=0; i<featureNames.length; i++) {
         var featureName = featureNames[i]
         var halt = featureRequirementBug
@@ -149,6 +150,20 @@ CollectionFunctions = (function(){
       }
       if (functionsForExport.map) functionsForExport.pluck = pluck
 
+      function isSorted(collection) {
+        var sorted = true
+        var previousItem = null
+        each(collection, function(item, i){
+          if (i>=1 && features.comparator(previousItem, item) < 0) {
+            sorted = false
+            return breaker
+          }
+          previousItem = item
+        })
+        return sorted
+      }
+      if (functionsForExport.each && feature("comparator")) functionsForExport.isSorted = isSorted
+
       function indexOf(collection, findMe) {
         var index = features.nothing()
         detect(collection, function(item, i){

spec/is_sorted_spec.js

@@ -0,0 +1,59 @@
+require("./spec_helper.js");
+
+describe("is sorted", function() {
+
+  var fArr = CollectionFunctions.Array.functions
+  var numberComparator = function(a,b){
+                           if (a==b) {
+                             return 0
+                           } else if (a<b) {
+                             return 1
+                           } else {
+                             return -1
+                           }
+                         }
+
+  it("determines whether a collection is sorted or not", function(){
+    var fMin = minimalArrayCF().appendFeatures({comparator:numberComparator}).functions
+
+    expect(fMin.isSorted([5,6])).toEqual(true)
+    expect(fMin.isSorted([5,6,7,8])).toEqual(true)
+    expect(fMin.isSorted([5,6,7,7,8])).toEqual(true)
+
+    expect(fMin.isSorted([2,3,1])).toEqual(false)
+    expect(fMin.isSorted([])).toEqual(true)
+    expect(fMin.isSorted([1])).toEqual(true)
+  })
+
+  describe("feature requirements", function(){
+
+    it("requires iterator and comparator", function(){
+      expect(CollectionFunctions({}).functions.
+        isSorted).toBeUndefined()
+
+      expect(CollectionFunctions({iterator:fArr.iterator}).functions.
+        isSorted).toBeUndefined()
+
+      expect(CollectionFunctions({iterator:fArr.iterator, comparator:numberComparator}).functions.
+        isSorted).toBeDefined()
+    })    
+
+  })
+
+  describe("cost", function() {
+
+    it("cost is the number of elements in the collection, is the collection is sorted", function(){      
+      var fMin = minimalArrayCF().appendFeatures({comparator:numberComparator}).functions
+      fMin.isSorted([5,6,7,8])
+      expect(fMin.lastCost()).toEqual(4)
+    })
+
+    it("cost is the number of elements to the first unsorted element, if unsorted", function(){      
+      var fMin = minimalArrayCF().appendFeatures({comparator:numberComparator}).functions
+      fMin.isSorted([5,7,6,8])
+      expect(fMin.lastCost()).toEqual(3)
+    })
+
+  })
+})
+