02_python_lists.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# List Data Structure Cheat Sheet\n",
    "\n",
    "This cheat sheet contains everything related to List DS."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "3\n"
     ]
    }
   ],
   "source": [
    "# Sequnce data structures\n",
    "# Contains Strings, int, other lists\n",
    "# Indexible and mutable\n",
    "\n",
    "emptyList = []\n",
    "\n",
    "lst = [1,2,3]\n",
    "\n",
    "lst2 = [[1,2], [3,4]]\n",
    "\n",
    "lst3 = [1, 2, 3, 'Jashan']\n",
    "\n",
    "# Length os list\n",
    "print(len(lst))\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3, 4, 5]\n",
      "[1, 2, 3, 4, 5, 5, 6, 7, 8]\n"
     ]
    }
   ],
   "source": [
    "# Append List and extend list\n",
    "\n",
    "lst = [1, 2, 3, 4]\n",
    "lst.append(5)\n",
    "print(lst)\n",
    "\n",
    "\n",
    "lst2 = [5,6,7,8]\n",
    "lst.extend(lst2)\n",
    "print(lst)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3, 4, 5]\n"
     ]
    }
   ],
   "source": [
    "# List insert\n",
    "\n",
    "\n",
    "lst = [1, 2, 4, 5]\n",
    "lst.insert(2,3)\n",
    "print(lst)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['one', 'three', 'four', 'two']\n"
     ]
    }
   ],
   "source": [
    "# List Remove: first occurence is removed\n",
    "\n",
    "lst = ['one', 'two', 'three', 'four', 'two']\n",
    "lst.remove('two')\n",
    "print(lst)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['one', 'three', 'four', 'two']\n",
      "three\n",
      "['one', 'four', 'two']\n"
     ]
    }
   ],
   "source": [
    "# List Delete: Based on index position\n",
    "\n",
    "lst = ['one', 'two', 'three', 'four', 'two']\n",
    "del lst[1]\n",
    "print(lst)\n",
    "\n",
    "# To get the deleted element use pop()\n",
    "\n",
    "a = lst.pop(1)\n",
    "print(a)\n",
    "print(lst)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3, 4, 5]\n",
      "[1, 2, 3, 4, 5]\n"
     ]
    }
   ],
   "source": [
    "# List related keywords: Use of if with in, not in\n",
    "\n",
    "# List reverse: lst.reverse()\n",
    "\n",
    "# List sorting:\n",
    "# 1. sorted(list, [reverse= True]) : original list remains same\n",
    "# 2. sort(): sort the list and stored in itself\n",
    "\n",
    "numbers = [5,1, 2, 3, 4]\n",
    "\n",
    "sortedList = sorted(numbers)\n",
    "print(sortedList)\n",
    "\n",
    "numbers.sort()\n",
    "print(numbers)\n",
    "\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "'<' not supported between instances of 'str' and 'int'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-12-1cf55db04750>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[0mlst\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;33m[\u001b[0m\u001b[1;36m1\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;36m20\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;34m'b'\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;36m5\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;34m'a'\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 2\u001b[1;33m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mlst\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0msort\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m              \u001b[1;31m# sort list with element of different datatypes.\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m: '<' not supported between instances of 'str' and 'int'"
     ]
    }
   ],
   "source": [
    "lst = [1, 20, 'b', 5, 'a']\n",
    "print(lst.sort())              # sort list with element of different datatypes.\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Original list:  [1, 2, 3, 4, 5, 6]\n"
     ]
    }
   ],
   "source": [
    "# List having multiple references\n",
    "\n",
    "lst = [1, 2, 3, 4, 5]\n",
    "lst2  = lst\n",
    "lst2.append(6)\n",
    "\n",
    "print(\"Original list: \", lst)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['one', 'two', 'three', 'four', 'five']\n"
     ]
    }
   ],
   "source": [
    "# String split to create a list\n",
    "\n",
    "s = \"one,two,three,four,five\"\n",
    "sLst = s.split(',')\n",
    "print(sLst)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['My', 'name', 'is', 'Jashan', 'Bansal.']\n"
     ]
    }
   ],
   "source": [
    "s = \"My name is Jashan Bansal.\"\n",
    "split_lst = s.split() # default split is white-character: space or tab\n",
    "print(split_lst)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# List indexing: [positive] and [negative]\n",
    "\n",
    "# List slicing: [start:end:step]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# List extend using +\n",
    "\n",
    "# List count: numbers.count(num)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# List Comprehension\n",
    "\n",
    "provide a concise way to create lists\n",
    "\n",
    "Make new lists where each element is the result of some operations applied to each member of another sequence or iterable, or to create a subsequence of those elements that satisfy a certain condition."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]\n"
     ]
    }
   ],
   "source": [
    "# Without list coprehension\n",
    "\n",
    "squares = []\n",
    "for i in range(10):\n",
    "    squares.append(i**2)\n",
    "print(squares)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]\n"
     ]
    }
   ],
   "source": [
    "# Using List Comprehension\n",
    "\n",
    "squares = [i**2 for i in range(10)]\n",
    "print(squares)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[-20, -40, 20, 40, 60]\n"
     ]
    }
   ],
   "source": [
    "lst = [-10, -20, 10, 20, 30]\n",
    "doubleLst = [i*2 for i in lst]\n",
    "print(doubleLst)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[10, 20, 30]\n"
     ]
    }
   ],
   "source": [
    "#filter the list to exclude negative numbers\n",
    "\n",
    "new_lst = [i for i in lst if i >= 0]\n",
    "print(new_lst)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25), (6, 36), (7, 49), (8, 64), (9, 81)]\n"
     ]
    }
   ],
   "source": [
    "#create a list of tuples like (number, square_of_number)\n",
    "\n",
    "newLst = [(i, i**2) for i in range(10)]\n",
    "print(newLst)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Nested List Comprehension"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]\n",
      "[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]\n"
     ]
    }
   ],
   "source": [
    "matrix = [\n",
    "    [1, 2, 3, 4],\n",
    "    [5, 6, 7, 8],\n",
    "    [9, 10, 11, 12]\n",
    "]\n",
    "\n",
    "#transpose of a matrix without list comprehension\n",
    "transposed = []\n",
    "for i in range(4):\n",
    "    lst = []\n",
    "    for row in matrix:\n",
    "        lst.append(row[i])\n",
    "    transposed.append(lst)\n",
    "\n",
    "print(transposed)\n",
    "\n",
    "#with list comprehension (Less Readable code) \n",
    "transposed = [[row[i] for row in matrix] for i in range(4)]\n",
    "print(transposed)\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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