12 - Sets.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Sets"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "-> A set is an unordered collection of items. Every element is unique (no duplicates).\n",
    "\n",
    "-> The set itself is mutable. We can add or remove items from it.\n",
    "\n",
    "-> Sets can be used to perform mathematical set operations like union, intersection, symmetric difference etc."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Set Creation"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "set([1, 2, 3])\n",
      "<type 'set'>\n"
     ]
    }
   ],
   "source": [
    "#set of integers\n",
    "s = {1, 2, 3}\n",
    "print(s)\n",
    "\n",
    "#print type of s \n",
    "print(type(s))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 2, 3, 4}\n"
     ]
    }
   ],
   "source": [
    "#set doesn't allow duplicates. They store only one instance.\n",
    "s = {1, 2, 3, 1, 4}\n",
    "print(s)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 2, 3}\n"
     ]
    }
   ],
   "source": [
    "#we can make set from a list\n",
    "s = set([1, 2, 3, 1])\n",
    "print(s)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "<class 'set'>\n"
     ]
    }
   ],
   "source": [
    "#initialize a set  with set() method\n",
    "s = set()\n",
    "\n",
    "print(type(s))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Add element to a Set"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "'set' object does not support indexing",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-4-c52fc339e293>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[1;32m      4\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      5\u001b[0m \u001b[0;31m#set object doesn't support indexing\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 6\u001b[0;31m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0ms\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m1\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;31m#will get TypeError\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mTypeError\u001b[0m: 'set' object does not support indexing"
     ]
    }
   ],
   "source": [
    "#we can add single element using add() method and \n",
    "#add multiple elements using update() method\n",
    "s = {1, 3}\n",
    "\n",
    "#set object doesn't support indexing\n",
    "print(s[1]) #will get TypeError"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 2, 3}\n"
     ]
    }
   ],
   "source": [
    "#add element\n",
    "s.add(2)\n",
    "print(s)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 2, 3, 5, 6}\n"
     ]
    }
   ],
   "source": [
    "#add multiple elements\n",
    "s.update([5, 6, 1])\n",
    "print(s)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 2, 3, 5, 6, 8, 9, 10}\n"
     ]
    }
   ],
   "source": [
    "#add list and set\n",
    "s.update([8, 9], {10, 2, 3})\n",
    "print(s)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Remove elements from a Set"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 2, 3, 4, 5}\n",
      "{1, 2, 3, 5}\n"
     ]
    }
   ],
   "source": [
    "#A particular item can be removed from set using methods, \n",
    "#discard() and remove().\n",
    "\n",
    "s = {1, 2, 3, 5, 4}\n",
    "print(s)\n",
    "\n",
    "s.discard(4)    #4 is removed from set s\n",
    "\n",
    "print(s)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 3, 5}\n"
     ]
    }
   ],
   "source": [
    "#remove an element \n",
    "s.remove(2)\n",
    "\n",
    "print(s)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "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-14-f37cc9806699>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0;31m#remove an element not present in a set s\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 2\u001b[0;31m \u001b[0ms\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mremove\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;36m7\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;31m# will get KeyError\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mKeyError\u001b[0m: 7"
     ]
    }
   ],
   "source": [
    "#remove an element not present in a set s\n",
    "s.remove(7) # will get KeyError"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 3, 5}\n"
     ]
    }
   ],
   "source": [
    "#discard an element not present in a set s\n",
    "s.discard(7)\n",
    "print(s)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{2, 3, 4, 5}\n"
     ]
    }
   ],
   "source": [
    "#we can remove item using pop() method\n",
    "\n",
    "s = {1, 2, 3, 5, 4}\n",
    "\n",
    "s.pop() #remove random element\n",
    "\n",
    "print(s)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{3, 4, 5}\n"
     ]
    }
   ],
   "source": [
    "s.pop() \n",
    "print(s)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "set()\n"
     ]
    }
   ],
   "source": [
    "s = {1, 5, 2, 3, 6}\n",
    "\n",
    "s.clear()   #remove all items in set using clear() method\n",
    "\n",
    "print(s)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Python Set Operations"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 2, 3, 4, 5, 6, 7}\n"
     ]
    }
   ],
   "source": [
    "set1 = {1, 2, 3, 4, 5}\n",
    "set2 = {3, 4, 5, 6, 7}\n",
    "\n",
    "#union of 2 sets using | operator\n",
    "\n",
    "print(set1 | set2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 2, 3, 4, 5, 6, 7}\n"
     ]
    }
   ],
   "source": [
    "#another way of getting union of 2 sets\n",
    "print(set1.union(set2))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{3, 4, 5}\n"
     ]
    }
   ],
   "source": [
    "#intersection of 2 sets using & operator\n",
    "print(set1 & set2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{3, 4, 5}\n"
     ]
    }
   ],
   "source": [
    "#use intersection function \n",
    "print(set1.intersection(set2))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 2}\n"
     ]
    }
   ],
   "source": [
    "#set Difference: set of elements that are only in set1 but not in set2\n",
    "\n",
    "print(set1 - set2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 2}\n"
     ]
    }
   ],
   "source": [
    "#use differnce function \n",
    "print(set1.difference(set2))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 2, 6, 7}\n"
     ]
    }
   ],
   "source": [
    "\"\"\"symmetric difference: set of elements in both set1 and set2 \n",
    "#except those that are common in both.\"\"\"\n",
    "\n",
    "#use ^ operator\n",
    "\n",
    "print(set1^set2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{1, 2, 6, 7}\n"
     ]
    }
   ],
   "source": [
    "#use symmetric_difference function\n",
    "print(set1.symmetric_difference(set2))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "set 'x' is subset of 'y' ? False\n",
      "set 'y' is subset of 'x' ? True\n"
     ]
    }
   ],
   "source": [
    "#find issubset()\n",
    "x = {\"a\",\"b\",\"c\",\"d\",\"e\"}\n",
    "y = {\"c\",\"d\"}\n",
    "\n",
    "print(\"set 'x' is subset of 'y' ?\", x.issubset(y)) #check x is subset of y\n",
    "\n",
    "#check y is subset of x\n",
    "print(\"set 'y' is subset of 'x' ?\", y.issubset(x))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Frozen Sets"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "collapsed": true
   },
   "source": [
    "Frozen sets has the characteristics of sets, but we can't be changed once it's assigned. While tuple are immutable lists, frozen sets are immutable sets"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Frozensets can be created using the function frozenset()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Sets being mutable are unhashable, so they can't be used as dictionary keys. On the other hand, frozensets are hashable and can be used as keys to a dictionary."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This datatype supports methods like copy(), difference(), intersection(), isdisjoint(), issubset(), issuperset(), symmetric_difference() and union(). Being immutable it does not have method that add or remove elements."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {},
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "'frozenset' object has no attribute 'add'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-28-8f5ea3d0c7e1>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[1;32m      3\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      4\u001b[0m \u001b[0;31m#try to add element into set1 gives an error\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 5\u001b[0;31m \u001b[0mset1\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0madd\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;36m5\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m: 'frozenset' object has no attribute 'add'"
     ]
    }
   ],
   "source": [
    "set1 = frozenset([1, 2, 3, 4])\n",
    "set2 = frozenset([3, 4, 5, 6])\n",
    "\n",
    "#try to add element into set1 gives an error\n",
    "set1.add(5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "'frozenset' object does not support indexing",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-27-8fc108f08ec8>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mset1\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m1\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;31m# frozen set doesn't support indexing\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mTypeError\u001b[0m: 'frozenset' object does not support indexing"
     ]
    }
   ],
   "source": [
    "print(set1[1]) # frozen set doesn't support indexing"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "frozenset({1, 2, 3, 4, 5, 6})\n"
     ]
    }
   ],
   "source": [
    "print(set1 | set2) #union of 2 sets"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "frozenset({3, 4})\n",
      "frozenset({3, 4})\n"
     ]
    }
   ],
   "source": [
    "#intersection of two sets\n",
    "print(set1 & set2)\n",
    "\n",
    "#or \n",
    "print(set1.intersection(set2))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "frozenset({1, 2, 5, 6})\n",
      "frozenset({1, 2, 5, 6})\n"
     ]
    }
   ],
   "source": [
    "#symmetric difference\n",
    "print(set1 ^ set2)\n",
    "\n",
    "#or\n",
    "print(set1.symmetric_difference(set2))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
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