diff --git a/.ipynb_checkpoints/timeit_tests-checkpoint.ipynb b/.ipynb_checkpoints/timeit_tests-checkpoint.ipynb
index 12ba838..8371eb3 100644
--- a/.ipynb_checkpoints/timeit_tests-checkpoint.ipynb
+++ b/.ipynb_checkpoints/timeit_tests-checkpoint.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:d5895f75b2ac58db150d7b521682366a447ffb2fb0b7db7e551edd40e6d1ab10"
+  "signature": "sha256:8dc4f91bc6a88e15ab0d25fac35b9a7645a7149b5ab4e1e15b2b372362e82ae2"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -855,63 +855,64 @@
      "collapsed": false,
      "input": [
       "import random\n",
-      "import copy\n",
       "import timeit\n",
+      "from collections import defaultdict\n",
       "\n",
       "\n",
-      "\n",
-      "def add_element_check1(my_dict, elements):\n",
+      "def add_element_check1(elements):\n",
+      "    d = dict()\n",
       "    for e in elements:\n",
-      "        if e not in my_dict:\n",
-      "            my_dict[e] = 1\n",
+      "        if e not in d:\n",
+      "            d[e] = 1\n",
       "        else:\n",
-      "            my_dict[e] += 1\n",
+      "            d[e] += 1\n",
+      "    return d\n",
       "            \n",
-      "def add_element_check2(my_dict, elements):\n",
+      "def add_element_check2(elements):\n",
+      "    d = dict()\n",
       "    for e in elements:\n",
-      "        if e not in my_dict:\n",
-      "            my_dict[e] = 0\n",
-      "        my_dict[e] += 1            \n",
-      "\n",
-      "def add_element_except(my_dict, elements):\n",
+      "        if e not in d:\n",
+      "            d[e] = 0\n",
+      "        d[e] += 1            \n",
+      "    return d\n",
+      "        \n",
+      "def add_element_except(elements):\n",
+      "    d = dict()\n",
       "    for e in elements:\n",
       "        try:\n",
-      "            my_dict[e] += 1\n",
+      "            d[e] += 1\n",
       "        except KeyError:\n",
-      "            my_dict[e] = 1\n",
+      "            d[e] = 1\n",
+      "    return d\n",
       "            \n",
+      "def add_element_defaultdict(elements):\n",
+      "    d = defaultdict(int)\n",
+      "    for e in elements:\n",
+      "        d[e] += 1\n",
+      "    return d\n",
       "\n",
       "random.seed(123)\n",
-      "rand_ints = [random.randrange(1, 10) for i in range(100)]\n",
-      "empty_dict = {}\n",
       "\n",
       "print('Results for 100 integers in range 1-10') \n",
-      "%timeit add_element_check1(copy.deepcopy(empty_dict), rand_ints)\n",
-      "%timeit add_element_check2(copy.deepcopy(empty_dict), rand_ints)\n",
-      "%timeit add_element_except(copy.deepcopy(empty_dict), rand_ints)\n",
-      "            \n",
-      "print('\\nResults for 1000 integers in range 1-10')            \n",
-      "rand_ints = [random.randrange(1, 10) for i in range(1000)]\n",
-      "empty_dict = {}\n",
+      "rand_ints = [random.randrange(1, 10) for i in range(100)]\n",
+      "%timeit add_element_check1(rand_ints)\n",
+      "%timeit add_element_check2(rand_ints)\n",
+      "%timeit add_element_except(rand_ints)\n",
+      "%timeit add_element_defaultdict(rand_ints)\n",
       "\n",
-      "%timeit add_element_check1(copy.deepcopy(empty_dict), rand_ints)\n",
-      "%timeit add_element_check2(copy.deepcopy(empty_dict), rand_ints)\n",
-      "%timeit add_element_except(copy.deepcopy(empty_dict), rand_ints)\n",
+      "print('\\nResults for 1000 integers in range 1-5')            \n",
+      "rand_ints = [random.randrange(1, 5) for i in range(1000)]\n",
+      "%timeit add_element_check1(rand_ints)\n",
+      "%timeit add_element_check2(rand_ints)\n",
+      "%timeit add_element_except(rand_ints)\n",
+      "%timeit add_element_defaultdict(rand_ints)\n",
       "\n",
       "print('\\nResults for 1000 integers in range 1-1000')            \n",
-      "rand_ints = [random.randrange(1, 10) for i in range(1000)]\n",
-      "empty_dict = {}\n",
-      "\n",
-      "%timeit add_element_check1(copy.deepcopy(empty_dict), rand_ints)\n",
-      "%timeit add_element_check2(copy.deepcopy(empty_dict), rand_ints)\n",
-      "%timeit add_element_except(copy.deepcopy(empty_dict), rand_ints)\n",
-      "\n",
-      "#\n",
-      "# Python 3.4.0\n",
-      "# MacOS X 10.9.2\n",
-      "# 2.5 GHz Intel Core i5\n",
-      "# 4 GB 1600 Mhz DDR3\n",
-      "#"
+      "rand_ints = [random.randrange(1, 1000) for i in range(1000)]\n",
+      "%timeit add_element_check1(rand_ints)\n",
+      "%timeit add_element_check2(rand_ints)\n",
+      "%timeit add_element_except(rand_ints)\n",
+      "%timeit add_element_defaultdict(rand_ints)"
      ],
      "language": "python",
      "metadata": {},
@@ -921,7 +922,7 @@
        "stream": "stdout",
        "text": [
         "Results for 100 integers in range 1-10\n",
-        "100000 loops, best of 3: 16.6 \u00b5s per loop"
+        "10000 loops, best of 3: 24.6 \u00b5s per loop"
        ]
       },
       {
@@ -929,7 +930,7 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "100000 loops, best of 3: 17.6 \u00b5s per loop"
+        "10000 loops, best of 3: 26.2 \u00b5s per loop"
        ]
       },
       {
@@ -937,7 +938,15 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "100000 loops, best of 3: 17.9 \u00b5s per loop"
+        "10000 loops, best of 3: 25.4 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "10000 loops, best of 3: 23 \u00b5s per loop"
        ]
       },
       {
@@ -946,8 +955,8 @@
        "text": [
         "\n",
         "\n",
-        "Results for 1000 integers in range 1-10\n",
-        "10000 loops, best of 3: 135 \u00b5s per loop"
+        "Results for 1000 integers in range 1-5\n",
+        "1000 loops, best of 3: 236 \u00b5s per loop"
        ]
       },
       {
@@ -955,7 +964,7 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "10000 loops, best of 3: 125 \u00b5s per loop"
+        "1000 loops, best of 3: 235 \u00b5s per loop"
        ]
       },
       {
@@ -963,7 +972,15 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "10000 loops, best of 3: 105 \u00b5s per loop"
+        "1000 loops, best of 3: 207 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "10000 loops, best of 3: 177 \u00b5s per loop"
        ]
       },
       {
@@ -973,7 +990,7 @@
         "\n",
         "\n",
         "Results for 1000 integers in range 1-1000\n",
-        "10000 loops, best of 3: 122 \u00b5s per loop"
+        "1000 loops, best of 3: 268 \u00b5s per loop"
        ]
       },
       {
@@ -981,7 +998,7 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "10000 loops, best of 3: 123 \u00b5s per loop"
+        "1000 loops, best of 3: 377 \u00b5s per loop"
        ]
       },
       {
@@ -989,7 +1006,15 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "10000 loops, best of 3: 104 \u00b5s per loop"
+        "1000 loops, best of 3: 511 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "1000 loops, best of 3: 410 \u00b5s per loop"
        ]
       },
       {
@@ -1000,14 +1025,21 @@
        ]
       }
      ],
-     "prompt_number": 13
+     "prompt_number": 16
     },
     {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
-      "### Conclusion\n",
-      "Interestingly, the `try-except` loop pays off if we have more elements (here: 1000 integers instead of 100) as dictionary keys to check. Also, it doesn't matter much whether the elements exist or do not exist in the dictionary, yet."
+      "### Conclusion"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "We see from the results that the `try-except` variant is faster than then the `if element in my_dict` alternative if we have a low number of unique elements (here: 1000 integers in the range 1-5), which makes sense: the `except`-block is skipped if an element is already added as a key to the dictionary. However, in this case the `collections.defaultdict` has even a better performance.  \n",
+      "However, if we are having a relative large number of unique entries(here: 1000 integers in range 1-1000), the `if element in my_dict` approach outperforms the alternative approaches."
      ]
     },
     {
diff --git a/benchmarks/timeit_tests.ipynb b/benchmarks/timeit_tests.ipynb
index 12ba838..8371eb3 100644
--- a/benchmarks/timeit_tests.ipynb
+++ b/benchmarks/timeit_tests.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:d5895f75b2ac58db150d7b521682366a447ffb2fb0b7db7e551edd40e6d1ab10"
+  "signature": "sha256:8dc4f91bc6a88e15ab0d25fac35b9a7645a7149b5ab4e1e15b2b372362e82ae2"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -855,63 +855,64 @@
      "collapsed": false,
      "input": [
       "import random\n",
-      "import copy\n",
       "import timeit\n",
+      "from collections import defaultdict\n",
       "\n",
       "\n",
-      "\n",
-      "def add_element_check1(my_dict, elements):\n",
+      "def add_element_check1(elements):\n",
+      "    d = dict()\n",
       "    for e in elements:\n",
-      "        if e not in my_dict:\n",
-      "            my_dict[e] = 1\n",
+      "        if e not in d:\n",
+      "            d[e] = 1\n",
       "        else:\n",
-      "            my_dict[e] += 1\n",
+      "            d[e] += 1\n",
+      "    return d\n",
       "            \n",
-      "def add_element_check2(my_dict, elements):\n",
+      "def add_element_check2(elements):\n",
+      "    d = dict()\n",
       "    for e in elements:\n",
-      "        if e not in my_dict:\n",
-      "            my_dict[e] = 0\n",
-      "        my_dict[e] += 1            \n",
-      "\n",
-      "def add_element_except(my_dict, elements):\n",
+      "        if e not in d:\n",
+      "            d[e] = 0\n",
+      "        d[e] += 1            \n",
+      "    return d\n",
+      "        \n",
+      "def add_element_except(elements):\n",
+      "    d = dict()\n",
       "    for e in elements:\n",
       "        try:\n",
-      "            my_dict[e] += 1\n",
+      "            d[e] += 1\n",
       "        except KeyError:\n",
-      "            my_dict[e] = 1\n",
+      "            d[e] = 1\n",
+      "    return d\n",
       "            \n",
+      "def add_element_defaultdict(elements):\n",
+      "    d = defaultdict(int)\n",
+      "    for e in elements:\n",
+      "        d[e] += 1\n",
+      "    return d\n",
       "\n",
       "random.seed(123)\n",
-      "rand_ints = [random.randrange(1, 10) for i in range(100)]\n",
-      "empty_dict = {}\n",
       "\n",
       "print('Results for 100 integers in range 1-10') \n",
-      "%timeit add_element_check1(copy.deepcopy(empty_dict), rand_ints)\n",
-      "%timeit add_element_check2(copy.deepcopy(empty_dict), rand_ints)\n",
-      "%timeit add_element_except(copy.deepcopy(empty_dict), rand_ints)\n",
-      "            \n",
-      "print('\\nResults for 1000 integers in range 1-10')            \n",
-      "rand_ints = [random.randrange(1, 10) for i in range(1000)]\n",
-      "empty_dict = {}\n",
+      "rand_ints = [random.randrange(1, 10) for i in range(100)]\n",
+      "%timeit add_element_check1(rand_ints)\n",
+      "%timeit add_element_check2(rand_ints)\n",
+      "%timeit add_element_except(rand_ints)\n",
+      "%timeit add_element_defaultdict(rand_ints)\n",
       "\n",
-      "%timeit add_element_check1(copy.deepcopy(empty_dict), rand_ints)\n",
-      "%timeit add_element_check2(copy.deepcopy(empty_dict), rand_ints)\n",
-      "%timeit add_element_except(copy.deepcopy(empty_dict), rand_ints)\n",
+      "print('\\nResults for 1000 integers in range 1-5')            \n",
+      "rand_ints = [random.randrange(1, 5) for i in range(1000)]\n",
+      "%timeit add_element_check1(rand_ints)\n",
+      "%timeit add_element_check2(rand_ints)\n",
+      "%timeit add_element_except(rand_ints)\n",
+      "%timeit add_element_defaultdict(rand_ints)\n",
       "\n",
       "print('\\nResults for 1000 integers in range 1-1000')            \n",
-      "rand_ints = [random.randrange(1, 10) for i in range(1000)]\n",
-      "empty_dict = {}\n",
-      "\n",
-      "%timeit add_element_check1(copy.deepcopy(empty_dict), rand_ints)\n",
-      "%timeit add_element_check2(copy.deepcopy(empty_dict), rand_ints)\n",
-      "%timeit add_element_except(copy.deepcopy(empty_dict), rand_ints)\n",
-      "\n",
-      "#\n",
-      "# Python 3.4.0\n",
-      "# MacOS X 10.9.2\n",
-      "# 2.5 GHz Intel Core i5\n",
-      "# 4 GB 1600 Mhz DDR3\n",
-      "#"
+      "rand_ints = [random.randrange(1, 1000) for i in range(1000)]\n",
+      "%timeit add_element_check1(rand_ints)\n",
+      "%timeit add_element_check2(rand_ints)\n",
+      "%timeit add_element_except(rand_ints)\n",
+      "%timeit add_element_defaultdict(rand_ints)"
      ],
      "language": "python",
      "metadata": {},
@@ -921,7 +922,7 @@
        "stream": "stdout",
        "text": [
         "Results for 100 integers in range 1-10\n",
-        "100000 loops, best of 3: 16.6 \u00b5s per loop"
+        "10000 loops, best of 3: 24.6 \u00b5s per loop"
        ]
       },
       {
@@ -929,7 +930,7 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "100000 loops, best of 3: 17.6 \u00b5s per loop"
+        "10000 loops, best of 3: 26.2 \u00b5s per loop"
        ]
       },
       {
@@ -937,7 +938,15 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "100000 loops, best of 3: 17.9 \u00b5s per loop"
+        "10000 loops, best of 3: 25.4 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "10000 loops, best of 3: 23 \u00b5s per loop"
        ]
       },
       {
@@ -946,8 +955,8 @@
        "text": [
         "\n",
         "\n",
-        "Results for 1000 integers in range 1-10\n",
-        "10000 loops, best of 3: 135 \u00b5s per loop"
+        "Results for 1000 integers in range 1-5\n",
+        "1000 loops, best of 3: 236 \u00b5s per loop"
        ]
       },
       {
@@ -955,7 +964,7 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "10000 loops, best of 3: 125 \u00b5s per loop"
+        "1000 loops, best of 3: 235 \u00b5s per loop"
        ]
       },
       {
@@ -963,7 +972,15 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "10000 loops, best of 3: 105 \u00b5s per loop"
+        "1000 loops, best of 3: 207 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "10000 loops, best of 3: 177 \u00b5s per loop"
        ]
       },
       {
@@ -973,7 +990,7 @@
         "\n",
         "\n",
         "Results for 1000 integers in range 1-1000\n",
-        "10000 loops, best of 3: 122 \u00b5s per loop"
+        "1000 loops, best of 3: 268 \u00b5s per loop"
        ]
       },
       {
@@ -981,7 +998,7 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "10000 loops, best of 3: 123 \u00b5s per loop"
+        "1000 loops, best of 3: 377 \u00b5s per loop"
        ]
       },
       {
@@ -989,7 +1006,15 @@
        "stream": "stdout",
        "text": [
         "\n",
-        "10000 loops, best of 3: 104 \u00b5s per loop"
+        "1000 loops, best of 3: 511 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "1000 loops, best of 3: 410 \u00b5s per loop"
        ]
       },
       {
@@ -1000,14 +1025,21 @@
        ]
       }
      ],
-     "prompt_number": 13
+     "prompt_number": 16
     },
     {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
-      "### Conclusion\n",
-      "Interestingly, the `try-except` loop pays off if we have more elements (here: 1000 integers instead of 100) as dictionary keys to check. Also, it doesn't matter much whether the elements exist or do not exist in the dictionary, yet."
+      "### Conclusion"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "We see from the results that the `try-except` variant is faster than then the `if element in my_dict` alternative if we have a low number of unique elements (here: 1000 integers in the range 1-5), which makes sense: the `except`-block is skipped if an element is already added as a key to the dictionary. However, in this case the `collections.defaultdict` has even a better performance.  \n",
+      "However, if we are having a relative large number of unique entries(here: 1000 integers in range 1-1000), the `if element in my_dict` approach outperforms the alternative approaches."
      ]
     },
     {