Added reduce calls from "mean" function

lib/function/statistics/mean.js

@@ -28,7 +28,7 @@ module.exports = function (math) {
       else if (arguments.length == 2) {
         // mean([a, b, c, d, ...], dim)
         // TODO: implement support for calculating the mean over specified dimension
-        throw new Error('Specifying a dimension is not yet implemented...');
+        return _nmean(arguments[0], arguments[1]-1);
       }
       else {
         throw new SyntaxError('Wrong number of parameters');
@@ -40,6 +40,25 @@ module.exports = function (math) {
     }
   };
 
+  /**
+   * Calculate the mean value in an n-dimensional array, returning a
+   * n-1 dimensional array
+   * @param {Array} array
+   * @param {Number} dimension
+   * @return {Number} mean
+   * @private
+   */
+  function _nmean(array, dim){
+	  var sum, len, tmp;
+	  sum = collection.reduce(array, dim, math.add);
+	  tmp = array;
+	  while(--dim){
+		  tmp = tmp[0];
+	  }
+	  len = tmp.length;
+	  return math.divide(sum/len);
+  };
+
   /**
    * Recursively calculate the mean value in an n-dimensional array
    * @param {Array} array

test/function/statistics/mean.test.js

@@ -36,6 +36,15 @@ describe('mean', function() {
     ])), 5);
   });
 
+  it('should return the mean value along a dimension on a matrix', function() {
+	  assert.deepEqual(math.mean([
+			  [2, 6],
+			  [4, 10]],2), [4, 7]);
+	  assert.deepEqual(math.mean([
+			  [2, 6],
+			  [4, 10]],1), [3, 8]);
+  });
+
   it('should throw an error if called with invalid number of arguments', function() {
     assert.throws(function() {math.mean()});
   });