udemy_data_structures/Section_1/List Comprehensions.ipynb

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 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Python List Comprehensions\n",
    "basic format: new_list = [transform sequence [filter] ]  \n",
    "© Joe James, 2019."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "import random"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**get values within a range**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "under_10: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]\n"
     ]
    }
   ],
   "source": [
    "under_10 = [x for x in range(10)]\n",
    "print('under_10: ' + str(under_10))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**get squared values**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "squares: [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]\n"
     ]
    }
   ],
   "source": [
    "squares = [x**2 for x in under_10]\n",
    "print('squares: ' + str(squares))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**get odd numbers using mod**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "odds: [1, 3, 5, 7, 9]\n"
     ]
    }
   ],
   "source": [
    "odds =  [x for x in range(10) if x%2 == 1]\n",
    "print('odds: ' + str(odds))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**get multiples of 10**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "ten_x: [0, 10, 20, 30, 40, 50, 60, 70, 80, 90]\n"
     ]
    }
   ],
   "source": [
    "ten_x = [x * 10 for x in range(10)]\n",
    "print('ten_x: ' + str(ten_x))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**get all numbers from a string**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "nums: 2073\n"
     ]
    }
   ],
   "source": [
    "s = 'I love 2 go t0 the store 7 times a w3ek.'\n",
    "nums = [x for x in s if x.isnumeric()]\n",
    "print('nums: ' + ''.join(nums))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**get index of a list item**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "index = 2\n"
     ]
    }
   ],
   "source": [
    "names = ['Cosmo', 'Pedro', 'Anu', 'Ray']\n",
    "idx = [k for k, v in enumerate(names) if v == 'Anu']\n",
    "print('index = ' + str(idx[0]))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**delete an item from a list**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['D', 'F', 'E', 'A', 'B', 'C'] ['D', 'F', 'E', 'A', 'B']\n"
     ]
    }
   ],
   "source": [
    "letters = [x for x in 'ABCDEF']\n",
    "random.shuffle(letters)\n",
    "letrs = [a for a in letters if a != 'C']\n",
    "print(letters, letrs)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**if-else condition in a comprehension**  \n",
    "must come before iteration."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "new list: [50, 30, 10, 18, 6, 70]\n"
     ]
    }
   ],
   "source": [
    "nums = [5, 3, 10, 18, 6, 7]\n",
    "new_list = [x if x%2 == 0 else 10*x for x in nums]\n",
    "print('new list: ' + str(new_list))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**nested loop iteration for 2D list**  \n",
    "b is the subsets, x is the values."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3, 4]\n"
     ]
    }
   ],
   "source": [
    "a = [[1,2],[3,4]]\n",
    "new_list = [x for b in a for x in b]\n",
    "print(new_list)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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