{"id":1383,"date":"2022-03-14T14:22:46","date_gmt":"2022-03-14T14:22:46","guid":{"rendered":"https:\/\/zerotobyte.com\/?p=1383"},"modified":"2022-03-14T14:22:48","modified_gmt":"2022-03-14T14:22:48","slug":"python-dictionary-count-items-keys-and-values","status":"publish","type":"post","link":"https:\/\/zerotobyte.com\/python-dictionary-count-items-keys-and-values\/","title":{"rendered":"Python Dictionary &#8211; Count Items, Keys and Values"},"content":{"rendered":"\n<p>Dictionary is a Python collection used to hold data as a <strong>key:value<\/strong> pairs, in some programming languages also known as a map. Keys are unique, acting as an index over the values they hold. In this post, we\u2019ll see how to count items, keys, and values inside a Python dictionary.<\/p>\n\n\n\n<p>The most convenient method to count how many pairs the Python dictionary contains is by using the <code>len()<\/code> method. <strong>Result is a number of distinct keys inside a dictionary, therefore this number also represents how many key:value pairs there are.<\/strong><\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Built-in items(), keys(), and values() methods<\/h2>\n\n\n\n<p>Python dictionary has some handful built-in methods that can help you look up or count different types of values:<\/p>\n\n\n\n<ul><li><code>dict.items()<\/code> &#8211; returns a list that contains tuples representing key:value pairs.<\/li><li><code>dict.keys()<\/code> &#8211; returns all dictionary keys as a list.<\/li><li><code>dict.values()<\/code> &#8211; returns all dictionary values as a list.<\/li><\/ul>\n\n\n\n<p>Let\u2019s see these methods in action.<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">>>> vehicles = {'vans': 2, 'cars': 12, 'buses': 3}\n\n>>> vehicles.items()\ndict_items([('vans', 2), ('cars', 12), ('buses', 3)])\n\n>>> vehicles.keys()\ndict_keys(['vans', 'cars', 'buses'])\n\n>>> vehicles.values()\ndict_values([2, 12, 3])<\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">How to count Python dictionary keys<\/h2>\n\n\n\n<p>There are multiple ways how to count keys in a Python dictionary. I will show you three ways:<\/p>\n\n\n\n<ul><li>Using <code>keys()<\/code> and <code>len()<\/code> method<\/li><li>Using <code>len()<\/code> method<\/li><li>Using custom function<\/li><\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Use <code>keys()<\/code> and <code>len()<\/code> to count dictionary items<\/h3>\n\n\n\n<p>Since <code>keys()<\/code> method already returns all distinct dictionary keys, you can use it in combination with the <code>len()<\/code> method to count different pairs inside a Python dictionary.\u00a0<\/p>\n\n\n\n<p>As you can see in the following example, this method returns a correct number of keys in dictionary.<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">>>> vehicles = {'vans': 2, 'cars': 12, 'buses': 3}\n\n>>> len(vehicles.keys())\n3<\/pre>\n\n\n\n<h3 class=\"wp-block-heading\">Use <code>len()<\/code> to count dictionary items<\/h3>\n\n\n\n<p>Although the above example is working, <strong>you could write it in shorter way by using only the <code>len()<\/code> method.<\/strong> The <code>len()<\/code> method returns the total length of a dictionary, or more precisely, the total number of items in the dictionary.<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">>>> vehicles = {'vans': 2, 'cars': 12, 'buses': 3}\n\n>>> len(vehicles)\n3<\/pre>\n\n\n\n<pre class=\"wp-block-verse\"><strong>NOTE<\/strong> - Using len() with keys() to count dictionary keys is slower than using len() only; therefore my recommendation is to use the latter.<\/pre>\n\n\n\n<h3 class=\"wp-block-heading\">Use custom function to count dictionary items<\/h3>\n\n\n\n<p>If you are in a need to write a custom function that will count a number of dictionary items, take a look at the following example. We used a simple for loop that iterates over tuples returned by the <code>items()<\/code> method. Each iteration increases the count value by 1. Here you can also add some additional logic if you need to.<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">def count_items(dictionary):\n  count = 0\n  for key, value in dictionary.items():\n    # Additional logic could go here\n    count += 1\n  return count\n\nvehicles = {'vans': 2, 'cars': 12, 'buses': 3}\ncount_items(vehicles)  # 3<\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">Bonus &#8211; Python dictionary count duplicate values<\/h2>\n\n\n\n<p>As a bonus to this post, let\u2019s see how to count the number of occurrences of each value inside a Python dictionary. To make it easier to understand, let\u2019s introduce the following example. We decided to survey 10 people, with the possibility of answering \u201cyes\u201d or \u201cno\u201d. We store each answer in a dictionary right under that user\u2019s name. The dictionary items look like this:<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">>>> answers = {'user1': 'yes', 'user2': 'no', 'user3': 'yes', 'user4': 'yes', 'user5': 'yes', 'user6': 'no', 'user7': 'yes', 'user8': 'no', 'user9': 'yes', 'user10': 'no'}<\/pre>\n\n\n\n<p>Now, to count how many times each answer was given, we can help ourselves with Python\u2019s built-in <code>collections<\/code> module. More precisely, we need a <a href=\"https:\/\/docs.python.org\/3\/library\/collections.html#collections.Counter\" target=\"_blank\" rel=\"noreferrer noopener\">Counter<\/a> class from the <code>collections<\/code> module. If we pass a list of values to the <strong>Counter<\/strong>, as a result we\u2019ll get key:value pairs that will represent each value and its number of occurrences.\u00a0<\/p>\n\n\n\n<p>In our example, we get a number of occurrences of each answer in a survey.<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"python\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">>>> from collections import Counter\n>>> Counter(answers.values())\nCounter({'yes': 6, 'no': 4})<\/pre>\n","protected":false},"excerpt":{"rendered":"<p>Dictionary is a Python collection used to hold data as a key:value pairs, in some programming languages also known as &#8230; <\/p>\n<p class=\"read-more-container\"><a title=\"Python Dictionary &#8211; Count Items, Keys and Values\" class=\"read-more button\" href=\"https:\/\/zerotobyte.com\/python-dictionary-count-items-keys-and-values\/#more-1383\" aria-label=\"More on Python Dictionary &#8211; 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