notebooks/3 - Python Objects Map Lambda List Comprehensions.ipynb

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   "cell_type": "markdown",
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   "source": [
    "### Python Objects, Map, Lambda, and List Comprehensions\n",
    "\n",
    "Jay Urbain, PhD\n",
    "\n",
    "6/26/2018"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Objects\n",
    "\n",
    "Example of a class in python:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Person:\n",
    "    company = 'nVidia' #a class variable\n",
    "\n",
    "    def set_name(self, new_name): #a method\n",
    "        self.name = new_name\n",
    "    def set_location(self, new_location):\n",
    "        self.location = new_location"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Dwight Diercks works for nVidia located at nVidia\n"
     ]
    }
   ],
   "source": [
    "person = Person()\n",
    "person.set_name('Dwight Diercks')\n",
    "person.set_location('2701 San Tomas Expressway Santa Clara, CA 95050')\n",
    "print('{} works for {} located at {}'.format(person.name, person.company, person.company))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Question\n",
    "\n",
    "- Define an object Student with one field `name` with a getter and setter for student name.\n",
    "- Set the student's name to 'Einstein'.\n",
    "- Get the student's name and format as shown in the solution cell."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Your answer here:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Student name: Einstein\n"
     ]
    },
    {
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       "    }\n",
       "    code_show = !code_show\n",
       "} \n",
       "\n",
       "$( document ).ready(code_toggle);\n",
       "</script>\n",
       "\n",
       "To show/hide the solution cell, click <a href=\"javascript:code_toggle()\">here</a>."
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   "source": [
    "from IPython.core.display import HTML\n",
    "class Student:\n",
    "\n",
    "    def set_name(self, new_name): #a method\n",
    "        self.name = new_name\n",
    "    def get_name(self):\n",
    "        return self.name\n",
    "\n",
    "student = Student()\n",
    "student.set_name('Einstein')\n",
    "print('Student name: {}'.format(student.get_name()) )\n",
    "\n",
    "HTML('''<script>\n",
    "code_show=true; \n",
    "function code_toggle() {\n",
    "    if (code_show){\n",
    "        $('div.cell.code_cell.rendered.selected div.input').hide();\n",
    "    } else {\n",
    "        $('div.cell.code_cell.rendered.selected div.input').show();\n",
    "    }\n",
    "    code_show = !code_show\n",
    "} \n",
    "\n",
    "$( document ).ready(code_toggle);\n",
    "</script>\n",
    "\n",
    "To show/hide the solution cell, click <a href=\"javascript:code_toggle()\">here</a>.''')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Map\n",
    "\n",
    "Maps return an iterator that applies a function to every item of one or more iterables.\n",
    "\n",
    "Example of `mapping` the `min` function between two lists."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "map"
      ]
     },
     "execution_count": 14,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# iterables, e.g., lists\n",
    "store1 = [10.00, 11.00, 12.34, 2.34]\n",
    "store2 = [9.00, 11.10, 12.34, 2.01]\n",
    "\n",
    "# map function min() to each item of iterables\n",
    "cheapest = map(min, store1, store2)\n",
    "\n",
    "# map returns a map iterator\n",
    "type(cheapest)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now literate through the map object to see the values."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
    "scrolled": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "9.0\n",
      "11.0\n",
      "12.34\n",
      "2.01\n"
     ]
    }
   ],
   "source": [
    "for item in cheapest:\n",
    "    print(item)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Lambda \n",
    "\n",
    "Lambda operator or lambda function is used for creating small, one-time anonymous function objects in Python. \n",
    "\n",
    "Works well with filter, and map.\n",
    "\n",
    "Simple function."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "3"
      ]
     },
     "execution_count": 16,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "def add_first_two(a, b, c):\n",
    "    return a+b\n",
    "\n",
    "add_first_two(1, 2, 3)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Same function as lambda function."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [],
   "source": [
    "my_function = lambda a, b, c : a + b"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "3"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "my_function(1, 2, 3)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Question\n",
    "\n",
    "Implement the following function as a lambda function."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def mod_it(x, mod_value):\n",
    "    if x % mod_value == 0:\n",
    "        return x\n",
    "    else:\n",
    "        return None\n",
    "    \n",
    "print(mod_it(7, 2))\n",
    "print(mod_it(6, 2))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "lambda_mod_it(7, 2) None\n",
      "lambda_mod_it(6, 2) 6\n"
     ]
    }
   ],
   "source": [
    "# Your work here\n",
    "\n",
    "lambda_mod_it = lambda x, mod_value: x if x % mod_value == 0 else None\n",
    "        \n",
    "print('lambda_mod_it(7, 2)', lambda_mod_it(7, 2))\n",
    "print('lambda_mod_it(6, 2)', lambda_mod_it(6, 2))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "lambda_mod_it(7, 2) None\n",
      "lambda_mod_it(6, 2) 6\n"
     ]
    },
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       "\n",
       "$( document ).ready(code_toggle);\n",
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       "\n",
       "To show/hide the solution cell, click <a href=\"javascript:code_toggle()\">here</a>."
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   "source": [
    "lambda_mod_it = lambda x, mod_value: x if x % mod_value == 0 else None\n",
    "\n",
    "print('lambda_mod_it(7, 2)', lambda_mod_it(7, 2))\n",
    "print('lambda_mod_it(6, 2)', lambda_mod_it(6, 2))\n",
    "\n",
    "HTML('''<script>\n",
    "code_show=true; \n",
    "function code_toggle() {\n",
    "    if (code_show){\n",
    "        $('div.cell.code_cell.rendered.selected div.input').hide();\n",
    "    } else {\n",
    "        $('div.cell.code_cell.rendered.selected div.input').show();\n",
    "    }\n",
    "    code_show = !code_show\n",
    "} \n",
    "\n",
    "$( document ).ready(code_toggle);\n",
    "</script>\n",
    "\n",
    "To show/hide the solution cell, click <a href=\"javascript:code_toggle()\">here</a>.''')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### List comprehension\n",
    "\n",
    "List comprehensions provide a concise way to create lists. \n",
    "\n",
    "They take the following form:  \n",
    "list_variable = [x for x in iterable]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Simple function to iterate from 0 to 999 and return the even numbers."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {},
   "outputs": [
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       " 976,\n",
       " 978,\n",
       " 980,\n",
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       " 986,\n",
       " 988,\n",
       " 990,\n",
       " 992,\n",
       " 994,\n",
       " 996,\n",
       " 998]"
      ]
     },
     "execution_count": 21,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "my_list = []\n",
    "for number in range(0, 1000):\n",
    "    if number % 2 == 0:\n",
    "        my_list.append(number)\n",
    "my_list"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now the same thing but with list comprehension."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "data": {
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      ]
     },
     "execution_count": 22,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "my_list = [number for number in range(0, 1000) if number % 2 == 0]\n",
    "        \n",
    "        \n",
    "        \n",
    "        \n",
    "        \n",
    "my_list = [number for number in range(0,1000) if number % 2 == 0]\n",
    "my_list"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Performance of list comprehensions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1.44 µs ± 7.09 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)\n"
     ]
    }
   ],
   "source": [
    "# standard function with list append\n",
    "def square_even(arr):\n",
    "    even_squares = []\n",
    "    for i in arr:\n",
    "        if i%2==0:\n",
    "            even_squares.append(i)\n",
    "\n",
    "%timeit square_even(range(1,11))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "2.76 µs ± 65.8 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)\n"
     ]
    }
   ],
   "source": [
    "# same function with list comprehension\n",
    "def square_even_lc(arr):\n",
    "    return [i**2 for i in arr if i%2==0]\n",
    "%timeit square_even_lc(range(1,11))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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