Find the Median of a List in Python

When you work with numerical list in Python, you may need to apply aggregation like finding the average. Most common operations are built-in in Python and no extra-code is needed. That being said, there is no function or method to retrieve the median of a list, a mathematical operation that is quite common even if the concept is less known as the average.

In this tutorial, we’ll see how you can extract the median of a list.

Quick reminder: what is a median?

While the average of a list is obtained by dividing the sum of the element of a list by its length, the median is somehow tricker to get. It is the middle value, which means that:

  • If the list has an odd number of elements, we just have to sort it and get the element in the middle
  • If the list has an even number of elements, the median is interpolated by taking the average of the two middle values

Some examples:

[1,2,3,4,5] #odd: median is 3 - position 2 [1,2,3,4,5,6] #even - median is (3+4)/2
Code language: PHP (php)

Create our own function

Using the definition we used before, we can create our own function to extract a median from a list. The code is pretty straightforward but if you want to understand it completely, keep in mind that:

  • While len() count the number of elements in a list, its index starts at 0. If you have 5 elements, the median is the element whose index is 2 (and not 3).
  • You need to use integer to access a value of a list by its index. Float will raise an error.
my_list = [3,4,5,1,2] my_other_list = [3,1,6,7,4,9] def get_median(l): #sort list l.sort() #if the number of elements is even if len(l) % 2 == 0: #get the two middle values value1 = l[int(len(l)/2)] value2 = l[int(len(l)/2-1)] #return the average return (value1+value2)/2 #if the number of elements is odd else: return l[int((len(l)+1)/2 - 1)] print(get_median(my_list)) print(get_median(my_other_list))
Code language: Python (python)


3 5.0
Code language: CSS (css)

Great, but we need to create our own function. If you don’t want to, you have an alternative solution.

Use statistics to get the median of a list

The library statistics comes with advanced functions, one of them allowing us to calculate a median.

my_list = [3,4,5,1,2] my_other_list = [3,1,6,7,4,9] from statistics import median print(median(my_list)) print(median(my_other_list))
Code language: JavaScript (javascript)


3 5.0
Code language: CSS (css)

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