{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "039de857",
   "metadata": {},
   "source": [
    "# Sets\n",
    "\n",
    "Sets are a new (to us!) data structure similar to lists in that they contain a bunch of other things. The two main distinguishing factors for sets are:\n",
    "\n",
    "1. Sets are _unordered_.\n",
    "2. Sets only include _unique_ values.\n",
    "\n",
    "As with all our data structures, we'll review how to create, query, and modify sets."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "b186c80b",
   "metadata": {},
   "source": [
    "## Creating sets\n",
    "\n",
    "New sets can be created either with the function `set()`, or with comma-separated items in between curly braces (`{}`). (This mirrors how we can create a new list either with `[1, 2, 3]` or using the `list()` function.)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "2c263bd7",
   "metadata": {},
   "outputs": [],
   "source": [
    "s1 = {1, 2, 3, 3, 1, 2, 1, 1, 1}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "a35be48d",
   "metadata": {},
   "outputs": [],
   "source": [
    "s2 = set([1, 2, 3])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "f60ddaa1",
   "metadata": {},
   "outputs": [],
   "source": [
    "s1 == s2"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "7ce14d42",
   "metadata": {},
   "source": [
    "**Note:** `{}` does _not_ create an empty set. Instead, it creates a new dictionary. We'll be covering dictionaries in the near future."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "ecae3f46",
   "metadata": {},
   "source": [
    "## Querying Sets\n",
    "\n",
    "In getting the data out of a set, here's where we start to see another key difference between sets and lists: ordering.\n",
    "\n",
    "Sets are defined as being unordered, which means it's an error to try and get the \"first\" item out. (If there's no order, what does \"first\" mean anyways?)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "02ec33e6",
   "metadata": {},
   "outputs": [],
   "source": [
    "s1 = {1, 2, 3, 4, 5, 6}\n",
    "s1[0]  # ERROR!!"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "193d350e",
   "metadata": {},
   "source": [
    "Instead, sets are normally worked on using collective operations. These set operations inherit from the world of _Math_ and evaluate to new sets:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "f4d55d23",
   "metadata": {},
   "outputs": [],
   "source": [
    "z = {5, 6, 7, 8}\n",
    "y = {1, 2, 3, 1, 5}\n",
    "k = z & y  # named version: z.intersection(y)\n",
    "j = z | y  # named version: z.union(y)\n",
    "m = y - z  # named: y.difference(z)\n",
    "n = z - y  # named: z.difference(y)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "13703051",
   "metadata": {},
   "outputs": [],
   "source": [
    "{1, 2, 3} & {2, 3, 4}  # intersection"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "811dbff2",
   "metadata": {},
   "outputs": [],
   "source": [
    "{1, 2, 3} | {2, 3, 4}  # union"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "357dc123",
   "metadata": {},
   "outputs": [],
   "source": [
    "{1, 2, 3} - {2, 3, 4}  # difference"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "b98cb512",
   "metadata": {},
   "source": [
    "## Modifying Sets\n",
    "\n",
    "When it comes to modifying sets, we typically just add or remove one element at a time."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "ead9c4fe",
   "metadata": {},
   "source": [
    "### Adding items"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "7f83272f",
   "metadata": {},
   "outputs": [],
   "source": [
    "s1 = {1, 2, 3}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "93183f44",
   "metadata": {},
   "outputs": [],
   "source": [
    "s1.add(4)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "a69104c1",
   "metadata": {},
   "outputs": [],
   "source": [
    "s1 = s1 | {5}"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "cdcfbb21",
   "metadata": {},
   "source": [
    "### Removing Items"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "c19c9877",
   "metadata": {},
   "outputs": [],
   "source": [
    "s1 = {1, 2, 3}"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "720971a1",
   "metadata": {},
   "outputs": [],
   "source": [
    "s1.remove(3)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "0b820fa2",
   "metadata": {},
   "outputs": [],
   "source": [
    "s1.discard(4)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "63f5dc11",
   "metadata": {},
   "outputs": [],
   "source": [
    "s1 = s1 - {2}"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "fb17208a",
   "metadata": {},
   "source": [
    "## Practice: Sets and Files\n",
    "\n",
    "Write a function that returns the number of unique words in a file."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "bf0f1fa2",
   "metadata": {},
   "outputs": [],
   "source": [
    "def unique_words(filename):\n",
    "    ..."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "c58cc9b9",
   "metadata": {},
   "source": [
    "Then, modify that function to only return the unique words that _aren't_ the common words: a, an, and, the. "
   ]
  },
  {
   "cell_type": "markdown",
   "id": "9784680f",
   "metadata": {},
   "source": []
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": ".venv",
   "language": "python",
   "name": "python3"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 3
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.13.3"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 5
}