How can you sort a list of dictionaries by a key contained in each dictionary using Python? Can you do it in 1 line to show off your friends? Of course!
To sort a list of dictionaries use the
sorted()
function with the
key
parameter set to a
lambda
function that uses the common key found in each dictionary that you want to sort the list by.
Previously I posted a task where I needed to sort a list after the second element onwards , in this article I’ll use the same techniques but apply this to a specific key in each dictionary.
Let’s start with a data set first:
>>> data = [{ 'Surname': 'Jones', 'Address': '1 Smith Way', '2020-Census': 5, '2016-Census': 3, '2012-Census': 2}, {'Surname': 'Smith', 'Address': '2 Smith Way', '2020-Census': 2, '2016-Census': 2, '2012-Census': 2}, {'Surname': 'Doe', 'Address': '3 Smith Way', '2020-Census': 5, '2016-Census': 4, '2012-Census': 4}]
How would you go about sorting this data if you needed the
data
list to be sorted by the
Dict
value represented by the
key
named
Surname
?
Thankfully the
sorted()
function comes in handy here. The parameters for the function are as follows:
sorted(iterable, key, reverse)
The first parameter
iterable
takes an iterable object such as a list, or even a dictionary (more on this later). The second parameter
key
takes a function or key value that instructs how to sort. And finally, the
reverse
parameter takes a boolean value on whether the sort is in descending order, by default this value is
False
.
The great thing about the
sorted
function is that it doesn’t mutate the list passed in at the first parameter. Therefore, we could achieve the desired result of sorting by the key name
Surname
by simply writing the following:
>>> sorted_data = sorted(data, key=lambda x:x['Surname'])
>>> print(sorted_data)
[{'Surname': 'Doe', 'Address': '3 Smith Way', '2020-Census': 5, '2016-Census': 4, '2012-Census': 4},
{'Surname': 'Jones', 'Address': '1 Smith Way', '2020-Census': 5, '2016-Census': 3, '2012-Census': 2},
{'Surname': 'Smith', 'Address': '2 Smith Way', '2020-Census': 2, '2016-Census': 2, '2012-Census': 2}]
The function used is a simple one-liner that performs the necessary task and uses a
lambda
function to get the job done.
What is a lambda function?
A lambda function is a function that simply performs operations without needing to be defined by a name.
In our working example, the lambda function accepts one parameter which we’ve labelled as
x
and the value being passed in is each
Dict
item from the
List
.
As the value is each
Dict
passed in we can then set the
key
that will be used to be the ordering condition, which we set as
x['Surname']
.
Summary
Sorting our list of
dictionaries in Python
can easily be achieved using the
sorted
function. By passing in our list as the first parameter, and using a
lambda
function as the
key
parameter we can achieve the desired result of getting a sorted list of dictionaries in Python in one line.
Explore my other article on how you can sort a simple dictionary by key or value using Python.
