{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "female-customs",
   "metadata": {},
   "source": [
    "# List Slicing"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "korean-management",
   "metadata": {},
   "source": [
    "List slicing is a way to get not just one element of a list, but a whole portion."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "canadian-young",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'c'"
      ]
     },
     "execution_count": 1,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L = [\"a\", \"b\", \"c\", \"d\", \"e\", \"f\"]\n",
    "L[2]"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "optional-february",
   "metadata": {},
   "source": [
    "`L[a:b]` means the portion of the list from index `a` (inclusive) to index `b` (exclusive)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "nasty-miracle",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['c', 'd', 'e']"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[2:5]"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "stylish-dealing",
   "metadata": {},
   "source": [
    "If you leave out `a`, it starts from the beginning of the list. If you leave out `b`, it goes to the end."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "short-charger",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['a', 'b', 'c', 'd']"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[:4]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "brown-marketplace",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['b', 'c', 'd', 'e', 'f']"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[1:]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "plain-matthew",
   "metadata": {},
   "outputs": [],
   "source": [
    "R = L[:] # a copy of the list!\n",
    "R = list(L) # another way to do the same thing"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "id": "de0bf479",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['a', 'b', 'c', 'd', 'e', 'f']\n",
      "['a', 'b', 'c', 'd', 'e', 'f']\n"
     ]
    }
   ],
   "source": [
    "L = ['a', 'b', 'c', 'd', 'e', 'f']\n",
    "R = list(L)\n",
    "print(L)\n",
    "print(R)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "id": "8f1d03c8",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['b', 'c', 'd', 'e', 'f']\n",
      "['a', 'b', 'c', 'd', 'e', 'f']\n"
     ]
    }
   ],
   "source": [
    "R.pop(0)\n",
    "print(R)\n",
    "print(L)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "8036217a",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['b', 'c', 'd', 'e', 'f']\n"
     ]
    }
   ],
   "source": [
    "print(L)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "73b9ef77",
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "markdown",
   "id": "deluxe-contributor",
   "metadata": {},
   "source": [
    "You can use a third piece `L[a:b:c]`, and `c` means how much to go up by each time."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "id": "mathematical-health",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['b', 'd']\n",
      "['b', 'd']\n"
     ]
    }
   ],
   "source": [
    "print(L[1:5:2])\n",
    "print([L[1], L[3]])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "id": "fffda418",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]\n"
     ]
    }
   ],
   "source": [
    "L = list(range(0, 21))\n",
    "print(L)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "id": "8dde5159",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 3, 6, 9, 12, 15, 18]"
      ]
     },
     "execution_count": 19,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[::3]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "individual-design",
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "id": "fleet-balloon",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0]"
      ]
     },
     "execution_count": 20,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[::-1]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "id": "eb2e6146",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[20, 18, 16, 14, 12, 10, 8, 6, 4, 2, 0]"
      ]
     },
     "execution_count": 21,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[::-2]"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "intense-questionnaire",
   "metadata": {},
   "source": [
    "Lastly, you can use negative indexing too. For example, to get the last 3 elements of a list:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "id": "fc1dd6f7",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "18"
      ]
     },
     "execution_count": 22,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[-3]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "id": "cubic-latest",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[18, 19, 20]"
      ]
     },
     "execution_count": 23,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[-3:]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "id": "8113eaa4",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[18, 19, 20]"
      ]
     },
     "execution_count": 24,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[len(L)-3:]"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "clinical-stewart",
   "metadata": {},
   "source": [
    "To get all except the last element:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "id": "2b2db509",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]"
      ]
     },
     "execution_count": 25,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[:len(L)-1]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "id": "olympic-salad",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]"
      ]
     },
     "execution_count": 26,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[:-1]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "4f0da356",
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "b9b900ad",
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "id": "48612df3",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]"
      ]
     },
     "execution_count": 27,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "id": "3e3a2dcc",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]"
      ]
     },
     "execution_count": 29,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[:round(len(L)/2)]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "id": "d2fc498e",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]"
      ]
     },
     "execution_count": 30,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[round(len(L)/2):]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 35,
   "id": "bfeb5d9f",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[0, 1, 2, 3, 4]"
      ]
     },
     "execution_count": 35,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[:5]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 36,
   "id": "e95a080a",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]"
      ]
     },
     "execution_count": 36,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "L[5:]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 33,
   "id": "1df5ad64",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "4"
      ]
     },
     "execution_count": 33,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "23 // 5"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 34,
   "id": "267d9ba6",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "4"
      ]
     },
     "execution_count": 34,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "int(23/5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "af026316",
   "metadata": {},
   "outputs": [],
   "source": []
  }
 ],
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