Python/Python Bisect.ipynb

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   "source": [
    "# Python Bisect Module\n",
    "Used to find the insertion point for adding an item to a sorted list.  \n",
    "Advantage: it's fast. Runs in O(log n).  \n",
    "[Documentation](https://docs.python.org/3/library/bisect.html)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "import bisect"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### bisect_left\n",
    "Finds the insertion point for an item in a sorted list, or the spot just left of any matches.  \n",
    "Works for list of ints, list of floats, list of strings."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
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     "text": [
      "2\n",
      "3\n",
      "2\n"
     ]
    }
   ],
   "source": [
    "a = [24, 33, 41, 41, 45, 50, 53, 59, 62, 66, 70]\n",
    "i = bisect.bisect_left(a, 41)\n",
    "print(i)\n",
    "\n",
    "b = [1.3, 2.2, 3.4, 4.6, 5.5, 6.9, 7.2, 8.4]\n",
    "j = bisect.bisect_left(b, 4.1)\n",
    "print(j)\n",
    "\n",
    "c = ['aaa', 'bbb', 'ccc', 'ddd']\n",
    "k = bisect.bisect_left(c, 'bug')\n",
    "print(k)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "If list is unsorted, results are unpredictable, but it still tries."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "2\n"
     ]
    }
   ],
   "source": [
    "a = [33, 24, 41, 41, 45, 50, 53, 59, 66, 62, 70]\n",
    "i = bisect.bisect_left(a, 30)\n",
    "print(i)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### insort_left\n",
    "This inserts an item into the list in the correct position."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[24, 33, 41, 41, 44, 45, 50, 53, 59, 62, 66, 70]\n"
     ]
    }
   ],
   "source": [
    "d = [24, 33, 41, 41, 45, 50, 53, 59, 62, 66, 70]\n",
    "bisect.insort_left(d, 44)\n",
    "print(d)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### bisect_right\n",
    "Just like bisect_left, but for matches it returns the spot just to the right of matches."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "4\n",
      "2\n",
      "3\n"
     ]
    }
   ],
   "source": [
    "a = [24, 33, 41, 41, 45, 50, 53, 59, 62, 66, 70]\n",
    "i = bisect.bisect_right(a, 41)\n",
    "print(i)\n",
    "\n",
    "b = [1.3, 2.2, 3.4, 4.6, 5.5, 6.9, 7.2, 8.4]\n",
    "j = bisect.bisect_right(b, 2.2)\n",
    "print(j)\n",
    "\n",
    "c = ['A', 'big', 'dog', 'runs', 'slowly']\n",
    "k = bisect.bisect_right(c, 'dog')\n",
    "print(k)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### insort_right\n",
    "Just like insort_left, but for matches it inserts to the right of the match."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[24, 33, 41, 41, 45, 46, 50, 53, 59, 62, 66, 70]\n"
     ]
    }
   ],
   "source": [
    "d = [24, 33, 41, 41, 45, 50, 53, 59, 62, 66, 70]\n",
    "bisect.insort_right(d, 46)\n",
    "print(d)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### A fast Find function for a Sorted List\n",
    "Find leftmost value greater than x in sorted list a"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "False\n"
     ]
    }
   ],
   "source": [
    "def find_next(a, x):\n",
    "    i = bisect.bisect_right(a, x)\n",
    "    if i < len(a):\n",
    "        return a[i]\n",
    "    return False\n",
    "\n",
    "print(find_next([10, 15, 20, 25, 30], 33))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### A simple get_grade function\n",
    "get_grade uses a list of cutoffs to split grades into 5 ranges, then uses the bisect index to return the corresponding grade. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['F', 'A', 'C', 'C', 'B', 'A', 'A']\n"
     ]
    }
   ],
   "source": [
    "def get_grade(score, cutoffs=[60, 70, 80, 90], grades='FDCBA'):\n",
    "    i = bisect.bisect_right(cutoffs, score)\n",
    "    return grades[i]\n",
    "\n",
    "grades = [get_grade(score) for score in [52, 99, 77, 70, 89, 90, 100]]\n",
    "print(grades)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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