group3_dicts_part1.ipynb

{
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Dictionaries\n",
    "\n",
    "A data structure organized as an associate array with a Key-Value Pair.\n",
    "The key is like the index of a list.\n",
    "\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Here we can make a short comparison between a list and a dictionary.\n",
    "We can grab a specific item by giving the index into the square brackets. Here we want to grab the second item in both list and dictionary."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "The second item in the list is:  1\n",
      "The second item in the dictionary is:  1\n"
     ]
    }
   ],
   "source": [
    "num_ls = [0,1,2]\n",
    "num_dict = {0:0, 1:1, 2:2}\n",
    "print(\"The second item in the list is: \", num_ls[1])\n",
    "print(\"The second item in the dictionary is: \", num_dict[1])\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Like lists it also not possible to call an index which is not included in the dictionary."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "ename": "IndexError",
     "evalue": "list index out of range",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mIndexError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-11-34064b77e515>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mnum_ls\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m7\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mIndexError\u001b[0m: list index out of range"
     ]
    }
   ],
   "source": [
    "num_ls[7]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "ename": "KeyError",
     "evalue": "7",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mKeyError\u001b[0m                                  Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-12-f345ad396a80>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mnum_dict\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m7\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mKeyError\u001b[0m: 7"
     ]
    }
   ],
   "source": [
    "num_dict[7]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We see the error messages for the same reason. Because we try to grab an item which is not in the list.\n",
    "The advantage of the dictionary is, that we can name the index like we want to. Almost.\n",
    "\n",
    "The key must be an immutable type as the key will be stored as hash in a fixed place in the memory.\n",
    "Example: We want to bring the following table into a dictionary, so we can ask for the capital of a german state.\n",
    "\n",
    "---\n",
    "\n",
    "|Key|Value|\n",
    "| --- | --- |\n",
    "|Hamburg|Hamburg|\n",
    "|Nordrhein-Westfalen|Düsseldorf|\n",
    "|Bayern|München|\n",
    "|Niedersachsen|Hannover|\n",
    "\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'Hamburg': 'Hamburg',\n",
       " 'Nordrhein-Westfalen': 'Düsseldorf',\n",
       " 'Bayern': 'München',\n",
       " 'Niedersachsen': 'Hanover'}"
      ]
     },
     "execution_count": 26,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "brd_capt_dict = {\"Hamburg\": \"Hamburg\", \"Nordrhein-Westfalen\": \"Düsseldorf\",\n",
    "                 \"Bayern\": \"München\", \"Niedersachsen\": \"Hanover\"}\n",
    "brd_capt_dict"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Questions\n",
    "* There is a typo in Hannover. How can we correct it?\n",
    "* Add another state. How would you do it?\n",
    "\n",
    "\n",
    "\n",
    "\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {},
   "outputs": [],
   "source": [
    "brd_capt_dict[\"Niedersachsen\"] = \"Hannover\"\n",
    "brd_capt_dict[\"Sachsen-Anhalt\"] = \"Magdeburg\""
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "* The Bavarians fulfill their dream and become independent. How do we delete them out of our dictionary?"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Answer\n",
    "\n",
    "\n",
    "\n",
    "\n",
    "```python\n",
    "del brd_capt_dict[\"Bayern\"]\n",
    "brd_capt_dict.pop(\"Bayern\")```\n",
    "...?\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  },
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   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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