feat: add counter ipynb
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b32128e01c
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287
notebooks/collections/counter.ipynb
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287
notebooks/collections/counter.ipynb
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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Counter\n",
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"\n",
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"Keeps track of number of times an item is added."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"metadata": {},
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"outputs": [],
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"source": [
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"from collections import Counter"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 3,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Counter({'b': 3, 'a': 2, 'c': 1})\n",
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"Counter({'c': 3, 'b': 2, 'a': 1})\n",
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"Counter({'b': 3, 'a': 2, 'c': 1})\n"
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]
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}
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],
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"source": [
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"print(Counter(['a', 'a', 'b', 'b', 'b', 'c']))\n",
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"\n",
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"# Notice that in the following cases of dict and kwargs, a new Counter\n",
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"# is created with the given number and no \"counting\" happens\n",
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"print(Counter({ 'a': 1, 'b': 2, 'c': 3}))\n",
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"print(Counter(a=2, b=3, c=1))"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"Empty counter can be created and later items added."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 4,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Counter({'a': 1})\n",
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"Counter({'a': 2})\n",
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"Counter({'b': 4, 'a': 2, 'c': 2})\n"
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]
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}
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],
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"source": [
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"empty = Counter()\n",
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"\n",
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"empty.update('a')\n",
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"print(empty)\n",
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"\n",
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"empty.update('a')\n",
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"print(empty)\n",
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"\n",
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"empty.update('bbbbcc')\n",
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"print(empty)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"Counts of an item can be retrieved by simply indexing."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 5,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Number of 'b': 4\n"
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]
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}
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],
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"source": [
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"print(\"Number of 'b':\", empty['b'])"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"❗️ Counter returns count of `0` for non-existent keys."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 8,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Number of 'z': 0\n"
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]
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}
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],
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"source": [
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"print(\"Number of 'z':\", empty['z'])"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### ⭐️ `most_common(n)`\n",
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"\n",
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"Returns `n` most common items as a sequence of pairs. If `n` is not provided, returns all in decreasing order."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 9,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Top 3 letters in the dictionary:\n",
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"e : 235331\n",
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"i : 201032\n",
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"a : 199554\n"
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]
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}
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],
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"source": [
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"c = Counter()\n",
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"\n",
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"with open('/usr/share/dict/words', 'r') as f:\n",
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" for line in f:\n",
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" c.update(line.rstrip().lower())\n",
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"\n",
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"print(\"Top 3 letters in the dictionary:\")\n",
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"for item, count in c.most_common(3):\n",
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" print(f\"{item} : {count}\")"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### Set and arithmetic operations"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 13,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"c1 + c2 = Counter({'a': 5, 'b': 5, 'e': 5, 'c': 3, 'd': 1})\n",
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"c1 - c2 = Counter({'e': 5, 'a': 3})\n",
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"c1 | c2 = Counter({'e': 5, 'a': 4, 'b': 3, 'c': 2, 'd': 1})\n",
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"c1 & c2 = Counter({'b': 2, 'a': 1, 'c': 1})\n"
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]
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}
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],
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"source": [
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"c1 = Counter(a=4, b=2, c=1, d=0, e=5)\n",
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"c2 = Counter(a=1, b=3, c=2, d=1)\n",
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"\n",
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"print(\"c1 + c2 =\", c1 + c2)\n",
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"print(\"c1 - c2 =\", c1 - c2) # NOTE: 0 counts and -ve counts are removed\n",
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"\n",
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"print(\"c1 | c2 =\", c1 | c2) # NOTE: Largest counts are preserved\n",
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"print(\"c1 & c2 =\", c1 & c2) # NOTE: Smallest counts are preserved"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"### Some extra APIs"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 14,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"a : 2\n",
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"a : 2\n",
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"b : 4\n",
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"b : 4\n",
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"b : 4\n",
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"b : 4\n",
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"c : 3\n",
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"c : 3\n",
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"c : 3\n",
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"d : 1\n"
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]
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}
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],
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"source": [
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"c = Counter('aabbbbcccd')\n",
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"\n",
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"# Get an iterator to loop through\n",
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"# NOTE: Does not return count == 0 items\n",
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"for el in c.elements():\n",
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" print(f\"{el} : {c[el]}\")"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 15,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Total items = 5\n"
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]
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}
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],
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"source": [
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"print(\"Total items =\", Counter('aaabb').total())"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": []
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}
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],
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"metadata": {
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"interpreter": {
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"hash": "9e0fd7424d8281b91a098a189d6ae37333be9d5a00ec75c9d3dec88c73652714"
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},
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"kernelspec": {
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"display_name": "Python 3.10.1 ('leetcode-yPz04C5d')",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.10.1"
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},
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"orig_nbformat": 4
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},
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"nbformat": 4,
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"nbformat_minor": 2
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}
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