# Find the Median Index in Python

5/5 - (1 vote)

🐍 Question: How to find the index of the median element in a Python list? Something like `argmedian()`?

In case you need a quick refresher, I have written this tutorial on finding the median itself (but not yet its index):

👉 Recommended: 6 Ways to Get the Median of a Python List

## Solution

A multi-liner solution to get the index of the median index is to first sort the list, take the mid-element from the sorted list, and search the index of the median using the `list.index()` method. This finds the index of the first occurrence of the median.

Here’s a code snippet that does that:

```def median_index(lst):
sorted_lst = sorted(lst)
mid = len(lst) // 2
median = sorted_lst[mid]
return lst.index(median)

print(median_index([10, 1, 5]))
# 2

print(median_index([10, 1, 5, 99, 100, 100]))
# 3

print(median_index([10, 1, 5, 99, 100, 100, 0]))
# 0
```

This is a Python function that takes a list of numbers as input and returns the index of the median element of the list. Here’s how the code works:

1. `def median_index(lst)`: This line defines a function called `median_index` that takes a list `lst` as input.
2. `sorted_lst = sorted(lst)`: This line creates a new list called `sorted_lst` that contains the same elements as the input list `lst`, but sorted in ascending order using the built-in `sorted()` function.
3. `mid = len(lst) // 2`: This line calculates the index of the median element in the original unsorted list `lst` by dividing the length of the list by 2 using the floor division operator `//`.
4. `median = sorted_lst[mid]`: This line assigns the value of the median element in the sorted list `sorted_lst` to a new variable called `median`. If the length of the list is odd, this will be the element at the index `mid`. If the length of the list is even, `mid` will be the index of the element to the left of the middle two elements, and `median` will be the leftmost of those two elements.
5. `return lst.index(median)`: This line returns the index of the median element in the original unsorted list `lst` by using the built-in `index()` function to find the index of the first occurrence of the `median` value in `lst`.
6. The `print()` statements at the end of the code call the `median_index()` function with different input lists and print the output to the console. For example, `print(median_index([10, 1, 5]))` will print `2` because the median element of the input list `[10, 1, 5]` is `5`, and its index in the list is `2`.

## Python One-Liner to Find the Index of Median

I love Python one-liners. ♥️

So, here’s the same code condensed in a single line of Python code that finds the index of the median element in the `lst` using `lst.index(sorted(lst)[len(lst)//2])`

```def median_index(lst):
return lst.index(sorted(lst)[len(lst)//2])```

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