A deep copy is overkill here.

The only destructive change to the supplied data array is to change its
ordering, so a shallow copy is enough to avoid clobbering it.

morris.coffee

@@ -25,10 +25,6 @@ class Morris.Line
     # bail if there's no data
     if @options.data is undefined or @options.data.length is 0
       return
-    else
-       # otherwise create a deep copy of the input data: we'll perform
-       # operations on it later so better not taint the user's data.
-       @options.data = clone(@options.data)
     @el.addClass 'graph-initialised'
     @precalc()
     @redraw()
@@ -79,7 +75,8 @@ class Morris.Line
   # Do any necessary pre-processing for a new dataset
   #
   precalc: ->
-    # sort data
+    # shallow copy & sort data
+    @options.data = @options.data.slice(0)
     @options.data.sort (a, b) => (a[@options.xkey] < b[@options.xkey]) - (b[@options.xkey] < a[@options.xkey])
     # extract labels
     @columnLabels = $.map @options.data, (d) => d[@options.xkey]
@@ -522,31 +519,6 @@ Morris.labelSeries = (dmin, dmax, pxwidth, specName, xLabelFormat) ->
     spec.incr(d)
   return ret
 
-# Perform a deep copy of the given object.
-# Source: http://coffeescriptcookbook.com/chapters/classes_and_objects/cloning
-clone = (obj) ->
-  if not obj? or typeof obj isnt 'object'
-    return obj
-
-  if obj instanceof Date
-    return new Date(obj.getTime())
-
-  if obj instanceof RegExp
-    flags = ''
-    flags += 'g' if obj.global?
-    flags += 'i' if obj.ignoreCase?
-    flags += 'm' if obj.multiline?
-    flags += 'y' if obj.sticky?
-    return new RegExp(obj.source, flags)
-
-  newInstance = new obj.constructor()
-
-  for key of obj
-    newInstance[key] = clone obj[key]
-
-  return newInstance
-
-
 minutesSpecHelper = (interval) ->
   span: interval * 60 * 1000
   start: (d) -> new Date(d.getFullYear(), d.getMonth(), d.getDate(), d.getHours())

morris.js

@@ -1,6 +1,6 @@
 // Generated by CoffeeScript 1.3.1
 (function() {
-  var $, Morris, clone, minutesSpecHelper, secondsSpecHelper,
+  var $, Morris, minutesSpecHelper, secondsSpecHelper,
     __bind = function(fn, me){ return function(){ return fn.apply(me, arguments); }; };
 
   $ = jQuery;
@@ -38,8 +38,6 @@
       }
       if (this.options.data === void 0 || this.options.data.length === 0) {
         return;
-      } else {
-        this.options.data = clone(this.options.data);
       }
       this.el.addClass('graph-initialised');
       this.precalc();
@@ -85,6 +83,7 @@
     Line.prototype.precalc = function() {
       var d, series_data, touchHandler, ykey, ymax, ymin, _i, _j, _k, _len, _len1, _ref, _ref1, _ref2, _results,
         _this = this;
+      this.options.data = this.options.data.slice(0);
       this.options.data.sort(function(a, b) {
         return (a[_this.options.xkey] < b[_this.options.xkey]) - (b[_this.options.xkey] < a[_this.options.xkey]);
       });
@@ -591,37 +590,6 @@
     return ret;
   };
 
-  clone = function(obj) {
-    var flags, key, newInstance;
-    if (!(obj != null) || typeof obj !== 'object') {
-      return obj;
-    }
-    if (obj instanceof Date) {
-      return new Date(obj.getTime());
-    }
-    if (obj instanceof RegExp) {
-      flags = '';
-      if (obj.global != null) {
-        flags += 'g';
-      }
-      if (obj.ignoreCase != null) {
-        flags += 'i';
-      }
-      if (obj.multiline != null) {
-        flags += 'm';
-      }
-      if (obj.sticky != null) {
-        flags += 'y';
-      }
-      return new RegExp(obj.source, flags);
-    }
-    newInstance = new obj.constructor();
-    for (key in obj) {
-      newInstance[key] = clone(obj[key]);
-    }
-    return newInstance;
-  };
-
   minutesSpecHelper = function(interval) {
     return {
       span: interval * 60 * 1000,

test/test.html

@@ -12,28 +12,28 @@
     module("Morris");
 
     test("Input data remains untouched", function () {
-        var my_data = [{x: 1, y: 1}, {x: 2, y: 2}];
-        var expected_data = [{x: 1, y: 1}, {x: 2, y: 2}];
-        Morris.Line({
-            element: "graph-placeholder",
-            data: my_data,
-            xkey: 'x',
-            ykeys: ['y'],
-            labels: ['dontcare']
-        });
-        deepEqual(my_data, expected_data);
+      var my_data = [{x: 1, y: 1}, {x: 2, y: 2}];
+      var expected_data = [{x: 1, y: 1}, {x: 2, y: 2}];
+      Morris.Line({
+        element: "graph-placeholder",
+        data: my_data,
+        xkey: 'x',
+        ykeys: ['y'],
+        labels: ['dontcare']
+      });
+      deepEqual(my_data, expected_data);
     });
 
-    test("Nicer error when the placeholder was not found.", function () {
-        var my_data = [{x: 1, y: 1}, {x: 2, y: 2}];
-        raises(function() {
-            Morris.Line({
-                element: "thisplacedoesnotexist",
-                data: my_data,
-                xkey: 'x',
-                ykeys: ['y'],
-                labels: ['dontcare']})
-        }, "Graph placeholder not found.");
+    test("Raise an error when the placeholder element is not found.", function () {
+      var my_data = [{x: 1, y: 1}, {x: 2, y: 2}];
+      raises(function() {
+        Morris.Line({
+          element: "thisplacedoesnotexist",
+          data: my_data,
+          xkey: 'x',
+          ykeys: ['y'],
+          labels: ['dontcare']})
+      }, "Graph placeholder not found.");
     });
 
     test("Morris.commas", function () {