Python Program to Sort the list according to the column using lambda

We often need to organize data based on a particular value, such as sorting rows in a dataset by a column. Python makes this task simple by using the sorted() function along with a lambda function. In this article, we will explore various approaches to Sorting the list according to column.

Let's understand this with a basic example:

a = [(2, 'B'), (1, 'A'), (3, 'C')]

# Sort by the first column
b = sorted(a, key=lambda x: x[0])

print(b) 

[(1, 'A'), (2, 'B'), (3, 'C')]

Explanation:

• lambda x: x[0] selects the first element of each tuple to sort by.
• The list is sorted in ascending order based on the first column.

Sort by First Column

To sort a list of lists or tuples by the first column (index 0), we can use the sorted() function with a lambda function as the sorting key.

a = [(3, 'fun!'), (1, 'Python'), (2, 'is')]

# Sort by first column (index 0)
sorted_data = sorted(a, key=lambda x: x[0])

print(sorted_data)  

[(1, 'Python'), (2, 'is'), (3, 'fun!')]

Explanation:

• x[0] extracts the first element of each tuple for sorting.
• The list is sorted in ascending order by default.

Sort by Second Column

To sort a list of lists or tuples by the second column (index 1), we can use the sorted() function with a lambda function specifying the second element.

a = [(3, 'fun!'), (1, 'Python'), (2, 'is')]

# Sort by second column (index 1)
sorted_data = sorted(a, key=lambda x: x[1])

print(sorted_data)  

[(1, 'Python'), (3, 'fun!'), (2, 'is')]

Sort a List of Lists by a Specific Column

To sort a list of lists by a specific column (index) in Python, we can use the sorted() function and specify the column index in the key parameter using a lambda function.

a = [[3, 50], [1, 70], [2, 60]]

# Sort by second column (index 1)
sorted_data = sorted(a, key=lambda x: x[1])

print(sorted_data) 

[[3, 50], [2, 60], [1, 70]]

Explanation:

• The lambda x: x[1] extracts the second column values.
• The list is sorted numerically by the second column.

Sort a list of tuple in Descending Order

We can use the sorted() function with the reverse=True parameter, and specify the column (or element) by which we want to sort using the key parameter (if necessary).

a = [(3, 'fun!'), (1, 'Python'), (2, 'is')]

# Sort by first column in descending order
sorted_data = sorted(a, key=lambda x: x[0], reverse=True)

print(sorted_data) 

[(3, 'fun!'), (2, 'is'), (1, 'Python')]

Explanation:

• The reverse=True argument sorts the data in descending order.