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How to Sort a Dictionary by Value in Python [Examples]

This article will show you how to sort a dictionary by the values it contains in the Python programming language. Code examples are included.

What is a Dictionary?

dictionary is one of Pythons built in variable types for storing data. Dictionaries are similar to associative arrays or hash tables in other languages.

A dictionary contains a collection of values or objects. Unlike lists and arrays, rather than their values being stored at a specific index (the ordered position in the sequence of stored values), values in a dictionary are identified by a key. This key can be descriptive, telling you what the purpose of the value as well as being used to retrieve it.

Essentially, a dictionary is a collection of key/value pairs, where the value is retrieved by accessing the key.

In PHP, this functionality is provided using associative arrays. In JavaScript, objects can be used in a similar manner to dictionaries as they too can store and retrieve data as key/value pairs.

Dictionaries are Ordered and Can Be Changed

From Python version 3.7 and onwards, dictionaries are ordered – the entries in the dictionary will remain in the order they appeared in when the dictionary was defined or the values were added.

Dictionaries are also changeable – you can add, remove and alter the items within.

How to Sort a Python Dictionary by Value

The above means that dictionaries can be sorted by re-creating the dictionary with the items in a new order based on their value.

Note that this only works for Python 3.7 and above – you should always ensure you are running up-to-date versions of Python for security and compatibility.

Below, a dictionary containing quantities is defined, and then sorted by each quantity:

myDictionary = {
    "apples": 3,
    "bananas": 6,
    "oranges": 2,
    "limes": 9

mySortedDictionary = {
    key: value for key, value in sorted(myDictionary.items(), key=lambda item: item[1])

myReverseSortedDictionary = {
    key: value for key, value in sorted(myDictionary.items(), key=lambda item: item[1], reverse=True)

The values of each new dictionary will now be in ascending and descending order.

So what’s going on here? The process is as follows:

  • A new variable is declared to hold the sorted dictionary
  • It is wrapped in {} (curly braces) – telling Python that the variable is a dictionary
  • Within this new dictionary, the results of the sorted() function are enumerated as key/value pairs
    • This enumeration goes through each item one by one and adds it to the wrapping dictionary
    • This enumeration is necessary as sorted() returns a list, so it cannot be used to create a new dictionary directly
  • The sorted() function sorts the values in the original dictionary, returning a list
    • Note that you cannot sort a list of mixed string or numerical values – it’s one or the other
    • The items() method of the original dictionary provides a list of the values from the original dictionary to be sorted
    • The lambda expression is used to set the comparison key to the value of each entry in the dictionary
      • A complete function can be used in its place for sorting by more complex methods
    • An optional reverse parameter can be set to reverse the sort order

There’s much more to sorting in Python than simple sorts on numerical value – check out the official documentation for more.

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I'm Brad, and I'm nearing 20 years of experience with Linux. I've worked in just about every IT role there is before taking the leap into software development. Currently, I'm building desktop and web-based solutions with NodeJS and PHP hosted on Linux infrastructure. Visit my blog or find me on Twitter to see what I'm up to.

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