diff --git a/arrays_strings/group_ordered/group_ordered_challenge.ipynb b/arrays_strings/group_ordered/group_ordered_challenge.ipynb
new file mode 100644
index 0000000..488ffad
--- /dev/null
+++ b/arrays_strings/group_ordered/group_ordered_challenge.ipynb
@@ -0,0 +1,168 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<small><i>This notebook was prepared by [wdonahoe](https://github.com/wdonahoe). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Challenge Notebook"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Implement a function that groups identical items based on their order in the list.\n",
+    "\n",
+    "* [Constraints](#Constraints)\n",
+    "* [Test Cases](#Test-Cases)\n",
+    "* [Algorithm](#Algorithm)\n",
+    "* [Code](#Code)\n",
+    "* [Unit Test](#Unit-Test)\n",
+    "* [Solution Notebook](#Solution-Notebook)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Constraints\n",
+    "\n",
+    "* Can we use extra data structures?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* group_ordered([1,2,1,3,2])     ->     [1,1,2,2,3]\n",
+    "* group_ordered(['a','b','a')    ->     ['a','a','b']\n",
+    "* group_ordered([1,1,2,3,4,5,2,1]->     [1,1,1,2,2,3,4,5]\n",
+    "* group_ordered([])              ->     []\n",
+    "* group_ordered([1])             ->     [1]\n",
+    "* group_ordered(None)            ->     None"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "Refer to the [solution notebook](https://github.com/donnemartin/interactive-coding-challenges/templates/foo_solution.ipynb).  If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "def group_ordered(list_in):\n",
+    "    # TODO: Implement me\n",
+    "    pass"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "**The following unit test is expected to fail until you solve the challenge.**"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+   ],
+   "source": [
+    "# %load test_group_ordered.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "class TestGroupOrdered(object):\n",
+    "\n",
+    "    def test_group_ordered(self,func):\n",
+    "\n",
+    "        assert_equal(func(None), None)\n",
+    "        assert_equal(func([]), [])\n",
+    "        assert_equal(func([1]), [1])\n",
+    "        assert_equal(func([1,2,1,3,2]),[1,1,2,2,3])\n",
+    "        assert_equal(func(['a','b','a']),['a','a','b'])\n",
+    "        assert_equal(func([1,1,2,3,4,5,2,1]),[1,1,1,2,2,3,4,5])\n",
+    "        assert_equal(func([1,2,3,4,3,4]),[1,2,3,3,4,4])\n",
+    "        print('Success: ' + func.__name__)\n",
+    "\n",
+    "def main():\n",
+    "    test = TestGroupOrdered()\n",
+    "    test.test_group_ordered(group_ordered)\n",
+    "    try:\n",
+    "        test.test_group_ordered(group_ordered_alt)\n",
+    "    except NameError:\n",
+    "        # Alternate solutions are only defined\n",
+    "        # in the solutions file\n",
+    "        pass\n",
+    "\n",
+    "if __name__ == '__main__':\n",
+    "    main()\n"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Solution Notebook\n",
+    "\n",
+    "Review the [solution notebook](https://github.com/donnemartin/interactive-coding-challenges/templates/foo_solution.ipynb) for a discussion on algorithms and code solutions."
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 2",
+   "language": "python",
+   "name": "python2"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 2
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython2",
+   "version": "2.7.6"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}
diff --git a/arrays_strings/group_ordered/group_ordered_solution.ipynb b/arrays_strings/group_ordered/group_ordered_solution.ipynb
new file mode 100644
index 0000000..4c9bc60
--- /dev/null
+++ b/arrays_strings/group_ordered/group_ordered_solution.ipynb
@@ -0,0 +1,250 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<small><i>This notebook was prepared by [wdonahoe](https://github.com/wdonahoe). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Solution Notebook"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Implement a function that groups identical items based on their order in the list.\n",
+    "\n",
+    "* [Constraints](#Constraints)\n",
+    "* [Test Cases](#Test-Cases)\n",
+    "* [Algorithm: Modified Selection Sort](#Algorithm: Modified Selection Sort)\n",
+    "* [Code: Modified Selection Sort](#Code: Modified Selection Sort)\n",
+    "* [Algorithm: Ordered Dict](#Algorithm: Ordered Dict)\n",
+    "* [Code: Ordered Dict](#Code:-Ordered-Dict)\n",
+    "* [Unit Test](#Unit-Test)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Constraints\n",
+    "\n",
+    "* Can we use extra data structures?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* group_ordered([1,2,1,3,2]) -> [1,1,2,2,3]\n",
+    "* group_ordered(['a','b','a') -> ['a','a','b']\n",
+    "* group_ordered([1,1,2,3,4,5,2,1]-> [1,1,1,2,2,3,4,5]\n",
+    "* group_ordered([]) -> []\n",
+    "* group_ordered([1]) -> [1]\n",
+    "* group_ordered(None) -> None\n"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm: Modified Selection Sort\n",
+    "\n",
+    "* Save the relative position of the first-occurence of each item in a list.\n",
+    "* Iterate through list of unique items.\n",
+    "    * Keep an outer index; scan rest of list, swapping matching items with outer index and incrementing outer index each time. \n",
+    "    \n",
+    "Complexity:\n",
+    "* Time: O(n^2)\n",
+    "* Space: O(n)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Code: Modified Selection Sort"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "def make_order_list(list_in):\n",
+    "    order_list = []\n",
+    "    for item in list_in:\n",
+    "        if item not in order_list:\n",
+    "            order_list.append(item)\n",
+    "    return order_list\n",
+    "\n",
+    "\n",
+    "def group_ordered(list_in):\n",
+    "    if list_in is None:\n",
+    "        return None\n",
+    "    order_list = make_order_list(list_in)\n",
+    "    current = 0\n",
+    "    for item in order_list:\n",
+    "        search = current + 1\n",
+    "        while True:\n",
+    "            try:\n",
+    "                if list_in[search] != item:\n",
+    "                    search += 1\n",
+    "                else:\n",
+    "                    current += 1\n",
+    "                    list_in[current], list_in[search] = list_in[search], list_in[current]\n",
+    "                    search += 1\n",
+    "            except IndexError:\n",
+    "                break\n",
+    "    return list_in"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm: Ordered Dict.\n",
+    "\n",
+    "* Use an ordered dict to track insertion order of each key\n",
+    "* Flatten list of values.\n",
+    "\n",
+    "Complexity:\n",
+    "\n",
+    "* Time: O(n)\n",
+    "* Space: O(n)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code: Ordered Dict"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "from collections import OrderedDict\n",
+    "\n",
+    "def group_ordered_alt(list_in):\n",
+    "    result = OrderedDict()\n",
+    "    for value in list_in:\n",
+    "        result.setdefault(value, []).append(value)\n",
+    "    return [v for group in result.values() for v in group]"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test\n",
+    "\n",
+    "#### The following unit test is expected to fail until you solve the challenge."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Overwriting test_group_ordered.py\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%writefile test_group_ordered.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "class TestGroupOrdered(object):\n",
+    "\n",
+    "    def test_group_ordered(self,func):\n",
+    "\n",
+    "        assert_equal(func(None), None)\n",
+    "        assert_equal(func([]), [])\n",
+    "        assert_equal(func([1]), [1])\n",
+    "        assert_equal(func([1,2,1,3,2]),[1,1,2,2,3])\n",
+    "        assert_equal(func(['a','b','a']),['a','a','b'])\n",
+    "        assert_equal(func([1,1,2,3,4,5,2,1]),[1,1,1,2,2,3,4,5])\n",
+    "        assert_equal(func([1,2,3,4,3,4]),[1,2,3,3,4,4])\n",
+    "        print('Success: ' + func.__name__)\n",
+    "\n",
+    "def main():\n",
+    "    test = TestGroupOrdered()\n",
+    "    test.test_group_ordered(group_ordered)\n",
+    "    try:\n",
+    "        test.test_group_ordered(group_ordered_alt)\n",
+    "    except NameError:\n",
+    "        # Alternate solutions are only defined\n",
+    "        # in the solutions file\n",
+    "        pass\n",
+    "\n",
+    "if __name__ == '__main__':\n",
+    "    main()\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Success: group_ordered\n"
+     ]
+    }
+   ],
+   "source": [
+    "%run -i test_group_ordered.py"
+   ]
+  }
+ ],
+ "metadata": {
+  "celltoolbar": "Edit Metadata",
+  "kernelspec": {
+   "display_name": "Python 2",
+   "language": "python",
+   "name": "python2"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 2
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython2",
+   "version": "2.7.6"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}
diff --git a/arrays_strings/group_ordered/test_group_ordered.py b/arrays_strings/group_ordered/test_group_ordered.py
new file mode 100644
index 0000000..653c3fd
--- /dev/null
+++ b/arrays_strings/group_ordered/test_group_ordered.py
@@ -0,0 +1,27 @@
+from nose.tools import assert_equal
+
+class TestGroupOrdered(object):
+
+    def test_group_ordered(self,func):
+
+        assert_equal(func(None), None)
+        assert_equal(func([]), [])
+        assert_equal(func([1]), [1])
+        assert_equal(func([1,2,1,3,2]),[1,1,2,2,3])
+        assert_equal(func(['a','b','a']),['a','a','b'])
+        assert_equal(func([1,1,2,3,4,5,2,1]),[1,1,1,2,2,3,4,5])
+        assert_equal(func([1,2,3,4,3,4]),[1,2,3,3,4,4])
+        print('Success: ' + func.__name__)
+
+def main():
+    test = TestGroupOrdered()
+    test.test_group_ordered(group_ordered)
+    try:
+        test.test_group_ordered(group_ordered_alt)
+    except NameError:
+        # Alternate solutions are only defined
+        # in the solutions file
+        pass
+
+if __name__ == '__main__':
+    main()
\ No newline at end of file