06-Python-Dictionaries.ipynb

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   "source": [
    "# 06-Dictionaries\n",
    "\n",
    "Hi Highlander!!!\n",
    "\n",
    "So far we've only seen how to store data types in sequences like storing characters in a string or items in a list. But what if we want to store information another way? Most programming languages have what is called a *hash table*, which is a key-item pairing. Under the hood, this allows for faster look up times of objects (at the \"cost\" of not being able to sort the data), practically it allows for us to store data with a mapping. \n",
    "\n",
    "The choice of deciding between sequences like a list and mappings like a dictionary often depends on the specific situation. As you become a stronger programmer, choosing the right storage format will become more intuitive.\n",
    "\n",
    "Let's cover the basics of dictionaries!"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Creating a Dictionary"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Let's create an empty dictionary\n",
    "d = {}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Verify the type of dictionary d\n",
    "type(d)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Make a dictionary with {} and : to signify a key and a value\n",
    "d = {'key1':'value1','key2':'value2'}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Call values by their key\n",
    "d['key1']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d['key2']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Another dictionary like a real dictionary\n",
    "animals = {'elefante': 'loxodonta africana',\n",
    "           'lobo': 'canis lupus',\n",
    "           'tigre': 'panthera tigris',\n",
    "           'ratón': 'mus musculus'\n",
    "          } "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### <font color='green'>Task:</font> Print the content of key *'perro'*\n",
    "Tip: \n",
    "1. Get the value of \"perro\" using the indexer \\['perro'\\]\n",
    "2. Use the print() and format() functions to print the value"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Adding New Key-Value Pairs"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d['new_key'] = 'new item'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### <font color='green'>Task:</font> Add two new elements in the *'animals'* dict"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Your code here ...\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "** Note: Dictionaries are unordered! *This may not be clear at first with smaller dictionaries, but as dictionaries get larger they won't retain order, which means they can not be sorted!* If you need order and the ability to sort, stick with a sequence, like a list! One last time -- A DICTIONARY IS AN UNORDERED MAPPING. THIS IS NOT IMMEDIATELY OBVIOUS WITH SMALL DICTIONARIES!**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d = {'a':1,'z':2}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d['new'] = 0"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d['za'] = 'hello'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Dictionaries are very flexible in the data types they can hold, they can hold numbers, strings, lists, and even other dictionaries!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d = {'k1':10,'k2':'stringy','k3':[1,2,3,],'k4':{'inside_key':100}}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d['k1']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d['k2']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d['k3']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d['k3'][0]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d['k4']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d['k4']['inside_key']"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### <font color='green'>Task:</font> Create your own dictionary named *'serpientes'* like this:\n",
    "```pyhton\n",
    "serpientes = {'víbora': 'vipera latastei', 'anaconda': 'eunectes marinus'}\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Your code here\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### <font color='green'>Task:</font> Insert the dictionary *'serpientes'* in the dictionary *'animals'*"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Your code here\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### If you look for an inexistent key, you get an error\n",
    "\n",
    "Error if you ask for a key that isn't there!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d['oops']"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### <font color='green'>Task:</font> Look for an inexistente animal in dictionary *'animals'*"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Your code here\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Keep dictionaries in mind when you need to create a mapping and don't care about order! \n",
    "\n",
    "For example:\n",
    "\n",
    "https://en.wikipedia.org/wiki/Secret_Service_code_name"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "code_names = {\"Obama\":'Renegade',\n",
    "             \"Bush\":'Trailblazer',\n",
    "             \"Reagan\":\"Rawhide\",\n",
    "             \"Ford\":\"Passkey\"}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "code_names[\"Ford\"]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Or populations:\n",
    "\n",
    "https://en.wikipedia.org/wiki/List_of_countries_by_population_(United_Nations)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "pop_in_mil = {\"Chile\":17,\n",
    "              \"USA\":323,\n",
    "              \"Germany\": 83,\n",
    "              \"India\": 1324}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "pop_in_mil[\"Chile\"]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Other methods"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "code_names.keys()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "code_names.values()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "code_names.items()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### <font color='green'>Task:</font> Apply the methods to the  dictionary *'animals'*\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Your code here ...\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Your code here ...\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Your code here ...\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Great work Highlanders, remember taht Dictionaries (and Lists) are one of the most useful data structures in any programing language and in Python too."
   ]
  }
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