feat: add counter ipynb

notebooks/collections/counter.ipynb

@@ -0,0 +1,287 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Counter\n",
+    "\n",
+    "Keeps track of number of times an item is added."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from collections import Counter"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Counter({'b': 3, 'a': 2, 'c': 1})\n",
+      "Counter({'c': 3, 'b': 2, 'a': 1})\n",
+      "Counter({'b': 3, 'a': 2, 'c': 1})\n"
+     ]
+    }
+   ],
+   "source": [
+    "print(Counter(['a', 'a', 'b', 'b', 'b', 'c']))\n",
+    "\n",
+    "# Notice that in the following cases of dict and kwargs, a new Counter\n",
+    "# is created with the given number and no \"counting\" happens\n",
+    "print(Counter({ 'a': 1, 'b': 2, 'c': 3}))\n",
+    "print(Counter(a=2, b=3, c=1))"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Empty counter can be created and later items added."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Counter({'a': 1})\n",
+      "Counter({'a': 2})\n",
+      "Counter({'b': 4, 'a': 2, 'c': 2})\n"
+     ]
+    }
+   ],
+   "source": [
+    "empty = Counter()\n",
+    "\n",
+    "empty.update('a')\n",
+    "print(empty)\n",
+    "\n",
+    "empty.update('a')\n",
+    "print(empty)\n",
+    "\n",
+    "empty.update('bbbbcc')\n",
+    "print(empty)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Counts of an item can be retrieved by simply indexing."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Number of 'b': 4\n"
+     ]
+    }
+   ],
+   "source": [
+    "print(\"Number of 'b':\", empty['b'])"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "❗️ Counter returns count of `0` for non-existent keys."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Number of 'z': 0\n"
+     ]
+    }
+   ],
+   "source": [
+    "print(\"Number of 'z':\", empty['z'])"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "### ⭐️ `most_common(n)`\n",
+    "\n",
+    "Returns `n` most common items as a sequence of pairs. If `n` is not provided, returns all in decreasing order."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Top 3 letters in the dictionary:\n",
+      "e : 235331\n",
+      "i : 201032\n",
+      "a : 199554\n"
+     ]
+    }
+   ],
+   "source": [
+    "c = Counter()\n",
+    "\n",
+    "with open('/usr/share/dict/words', 'r') as f:\n",
+    "    for line in f:\n",
+    "        c.update(line.rstrip().lower())\n",
+    "\n",
+    "print(\"Top 3 letters in the dictionary:\")\n",
+    "for item, count in c.most_common(3):\n",
+    "    print(f\"{item} : {count}\")"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "### Set and arithmetic operations"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 13,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "c1 + c2 = Counter({'a': 5, 'b': 5, 'e': 5, 'c': 3, 'd': 1})\n",
+      "c1 - c2 = Counter({'e': 5, 'a': 3})\n",
+      "c1 | c2 = Counter({'e': 5, 'a': 4, 'b': 3, 'c': 2, 'd': 1})\n",
+      "c1 & c2 = Counter({'b': 2, 'a': 1, 'c': 1})\n"
+     ]
+    }
+   ],
+   "source": [
+    "c1 = Counter(a=4, b=2, c=1, d=0, e=5)\n",
+    "c2 = Counter(a=1, b=3, c=2, d=1)\n",
+    "\n",
+    "print(\"c1 + c2 =\", c1 + c2)\n",
+    "print(\"c1 - c2 =\", c1 - c2) # NOTE: 0 counts and -ve counts are removed\n",
+    "\n",
+    "print(\"c1 | c2 =\", c1 | c2) # NOTE: Largest counts are preserved\n",
+    "print(\"c1 & c2 =\", c1 & c2) # NOTE: Smallest counts are preserved"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "### Some extra APIs"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 14,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "a : 2\n",
+      "a : 2\n",
+      "b : 4\n",
+      "b : 4\n",
+      "b : 4\n",
+      "b : 4\n",
+      "c : 3\n",
+      "c : 3\n",
+      "c : 3\n",
+      "d : 1\n"
+     ]
+    }
+   ],
+   "source": [
+    "c = Counter('aabbbbcccd')\n",
+    "\n",
+    "# Get an iterator to loop through\n",
+    "# NOTE: Does not return count == 0 items\n",
+    "for el in c.elements():\n",
+    "    print(f\"{el} : {c[el]}\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 15,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Total items = 5\n"
+     ]
+    }
+   ],
+   "source": [
+    "print(\"Total items =\", Counter('aaabb').total())"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  }
+ ],
+ "metadata": {
+  "interpreter": {
+   "hash": "9e0fd7424d8281b91a098a189d6ae37333be9d5a00ec75c9d3dec88c73652714"
+  },
+  "kernelspec": {
+   "display_name": "Python 3.10.1 ('leetcode-yPz04C5d')",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.10.1"
+  },
+  "orig_nbformat": 4
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}