Merge pull request #59 from raichoo/master

Add `partition` to Data.Array

Author: garyb

.jshintrc

@@ -5,7 +5,7 @@
   "freeze": true,
   "funcscope": true,
   "futurehostile": true,
-  "globalstrict": true,
+  "strict": "global",
   "latedef": true,
   "maxparams": 1,
   "noarg": true,

docs/Data/Array.md

@@ -101,6 +101,8 @@ termination.
 null :: forall a. Array a -> Boolean
 ```
 
+Test whether an array is empty.
+
 #### `length`
 
 ``` purescript
@@ -115,6 +117,14 @@ Get the number of elements in an array.
 cons :: forall a. a -> Array a -> Array a
 ```
 
+Attaches an element to the front of an array, creating a new array.
+
+```purescript
+cons 1 [2, 3, 4] = [1, 2, 3, 4]
+```
+
+Note, the running time of this function is `O(n)`.
+
 #### `(:)`
 
 ``` purescript
@@ -158,6 +168,10 @@ determine the ordering of elements.
 head :: forall a. Array a -> Maybe a
 ```
 
+Get the first element in an array, or `Nothing` if the array is empty
+
+Running time: `O(1)`.
+
 #### `last`
 
 ``` purescript
@@ -215,6 +229,9 @@ f arr = case uncons arr of
 index :: forall a. Array a -> Int -> Maybe a
 ```
 
+This function provides a safe way to read a value at a particular index
+from an array.
+
 #### `(!!)`
 
 ``` purescript
@@ -309,6 +326,8 @@ index is out-of-bounds.
 reverse :: forall a. Array a -> Array a
 ```
 
+Reverse an array, creating a new array.
+
 #### `concat`
 
 ``` purescript
@@ -335,6 +354,16 @@ filter :: forall a. (a -> Boolean) -> Array a -> Array a
 Filter an array, keeping the elements which satisfy a predicate function,
 creating a new array.
 
+#### `partition`
+
+``` purescript
+partition :: forall a. (a -> Boolean) -> Array a -> { yes :: Array a, no :: Array a }
+```
+
+Partition an array using a predicate function, creating a set of
+new arrays. One for the values satisfying the predicate function
+and one for values that don't.
+
 #### `filterM`
 
 ``` purescript
@@ -372,6 +401,8 @@ a value, creating a new array.
 sort :: forall a. (Ord a) => Array a -> Array a
 ```
 
+Sort the elements of an array in increasing order, creating a new array.
+
 #### `sortBy`
 
 ``` purescript
@@ -387,6 +418,8 @@ the specified partial ordering, creating a new array.
 slice :: forall a. Int -> Int -> Array a -> Array a
 ```
 
+Extract a subarray by a start and end index.
+
 #### `take`
 
 ``` purescript

src/Data/Array.js

@@ -174,6 +174,21 @@ exports.filter = function (f) {
   };
 };
 
+exports.partition = function (f) {
+  return function (xs) {
+    var yes = [];
+    var no  = [];
+    for (var i = 0; i < xs.length; i++) {
+      var x = xs[i];
+      if (f(x))
+        yes.push(x);
+      else
+        no.push(x);
+    }
+    return { yes: yes, no: no };
+  };
+};
+
 //------------------------------------------------------------------------------
 // Sorting ---------------------------------------------------------------------
 //------------------------------------------------------------------------------

src/Data/Array.purs

@@ -64,6 +64,7 @@ module Data.Array
   , concat
   , concatMap
   , filter
+  , partition
   , filterM
   , mapMaybe
   , catMaybes
@@ -369,6 +370,13 @@ concatMap = flip bind
 -- | creating a new array.
 foreign import filter :: forall a. (a -> Boolean) -> Array a -> Array a
 
+-- | Partition an array using a predicate function, creating a set of
+-- | new arrays. One for the values satisfying the predicate function
+-- | and one for values that don't.
+foreign import partition :: forall a. (a -> Boolean)
+                         -> Array a
+                         -> { yes :: Array a, no :: Array a }
+
 -- | Filter where the predicate returns a monadic `Boolean`.
 -- |
 -- | ```purescript