Python sort list of list by index

Sort list of lists by index of inner Python list

In this article, we are going to learn how to Sort list of lists by index of inner Python list. We will use the nested lists and then we will sort the lists based on the indexes in the nested list. The user will be able to give input on which index he wants to sort on. We will make use of the below python functions. We will write code by using both functions in a different logic.

Syntax

sorted(iterable, key, reverse)

Parameters: sorted takes three parameters of which two are optional.

• Iterable: sequence (list, tuple, string) or collection (dictionary, set, frozenset) or any other iterator that needs to be sorted.
• Key(optional): A function that would serve as a key or a basis of sort comparison.
• Reverse(optional): If True, then the iterable would be sorted in reverse (descending) order, by default it is set as False.
• Return: Returns a list with elements in sorted order.

Python sort() Function syntax:-

list.sort(reverse=True|False, key=myFunc)

Parameter Description

• reverses Optional. reverse=True will sort the list descending. Default is reverse=False
• key Optional. A function to specify the sorting criteria(s)

1. Sort list of lists by index of inner Python list

• First, create a List of lists.
• Now enter the index through what you want to sort in a list of lists.
• In the method1 I use the sorted and lambda function
• In the lambda function, we pass the index of the inner list by which sorting is done.
• The sorted function returns a list so we can store it in a variable- called new_list and then print it.
• In method 2 I use another inbuilt method for sorting called sort () which is only used for lists.
• In the sort method, I pass the lambda function and index for sorting the inner list.
• The sort method updates the current list so no need to create a new list.

OrgList=[['Rahul', 56, 118],['Vidhi', 32, 120],['Nanoha', 71, 67],['Akkira', 13, 81]] Index=int(input("Enter Index(0-2): ")) if Index==0: print("Sorting Performing By Index 0") elif Index==1: print("Sorting Performing By Index 1.") else: print("Sorting Performing By Index 2") print("Method 1") sorted_list = sorted(OrgList,key=lambda x:x[Index]) print(sorted_list) print("Method 2") OrgList.sort(key=lambda x:x[Index]) print(OrgList)

Enter Index(0-2): 1
Sorting Performing By Index 1.
Method 1
[[‘Akkira’, 13, 81], [‘Vidhi’, 32, 120], [‘Rahul’, 56, 118], [‘Nanoha’, 71, 67]]Method 2
[[‘Akkira’, 13, 81], [‘Vidhi’, 32, 120], [‘Rahul’, 56, 118], [‘Nanoha’, 71, 67]]

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Python Sort List of Lists

How to sort a list of lists in python? Sorting a list of lists in Python is a powerful feature that allows you to sort the inner lists based on a specific element, known as the sorting key. This can be useful in many scenarios, such as when you want to sort a list of records based on a specific field or attribute.

You can sort a list of lists in Python using the sorted() function. By default, sorted() sorts the elements of a list in ascending order. To sort a list of lists based on a specific element in each sublist, you can pass a custom sorting function to the key argument. In this article, I will explain how to sort a list of lists in Python by using the sort() method, and sorted() function with examples.

1. Quick Examples of Sort List of Lists

If you are in a hurry, below are some quick examples of how to sort a list of lists.

 # Quick examples of sort list of lists # Example 1: Use sorted() function to sort a list of lists lists = [[93, 6], [72, 9], [35, 2]] print("Sorted Lists based on index 0: % s" % (sorted(lists, key=itemgetter(0)))) lists = [[2500, 'Spark'], [2200, 'Hadoop'], [3000, 'Python']] print("Sorted Lists based on index 1: % s" % (sorted(lists, key=itemgetter(1)))) # Example 2: use the itemgetter() function # sort the list of lists based on multiple elements lists = [[93, 6], [72, 9], [35, 2]] sorted_list = sorted(lists, key=itemgetter(0, 1)) # Example 3: use the itemgetter() function # sort a list of lists in descending order lists = [[1000, 'Java'], [2500, 'Spark'], [2200, 'Hadoop'], [3000, 'Python']] sorted_list = sorted(lists, key=itemgetter(1), reverse=True) # Example 4: Sort a list of lists Using lambda expression # along with the sorted() lists = [[1000, 'Java'], [2500, 'Spark'], [2200, 'Hadoop'], [3000, 'Python']] sorted_list = sorted(lists, key=lambda x:x[0]) # Example 5: Sort a list of lists using lambda # along with sorted() method sorted_list = sorted(lists, key=lambda x:x[1]) # Example 6: Sorted list of lists in descending sorted_list = sorted(lists, key=lambda x: x[1], reverse=True) # Example 7: Sort a list of lists # using sort() function lists = [[93, 6], [72, 9], [35, 2]] lists.sort() # Example 8: Sort list of lists # in descending order lists.sort(reverse=True) # Example 9: Sort list of lists in key=len lists = [[3, 4, 5], [1, 2], [6, 7, 8, 9]] lists.sort(key=len) 

2. Sort a List of Lists Using itemgetter() Function

You can use the itemgetter() function from the operator module as a key function when sorting a list of lists in Python. The itemgetter() function returns a callable object that accesses the specified item(s) of an object, which can be used to sort a list of lists.

For example, the itemgetter() function along with the sorted() function sorts a list of lists based on the first element of each sub-list.

 # Import from operator import itemgetter # Using sorted() function # Use itemgetter() function to select the position in the list to sort lists = [[93, 6], [72, 9], [35, 2]] print("Sorted Lists based on index 0: % s" % (sorted(lists, key=itemgetter(0)))) # Sort by second element of the inner list lists = [[2500, 'Spark'], [2200, 'Hadoop'], [3000, 'Python']] print("Sorted Lists based on index 1: % s" % (sorted(lists, key=itemgetter(1)))) # Output: # Sorted Lists based on index 0: [[35, 2], [72, 9], [93, 6]] # Sorted Lists based on index 1: [[2200, 'Hadoop'], [3000, 'Python'], [2500, 'Spark']] 

You can also use the itemgetter() function to sort the list of lists based on multiple elements. For example, if you want to sort the list based on the second element of each sub-list in case of a tie with the first element, you can modify the key function.

 # Sort the list of lists based on multiple elements lists = [[93, 6], [72, 9], [35, 2]] sorted_list = sorted(lists, key=itemgetter(0, 1)) print(sorted_list) # Output: # [[35, 2], [72, 9], [93, 6]] 

To sort a list of lists in descending order, you can pass the reverse=True argument to the sorted() function. For example, this tells the sorted() function to sort the list in reverse order.

 # Sort a list of lists in descending order lists = [[1000, 'Java'], [2500, 'Spark'], [2200, 'Hadoop'], [3000, 'Python']] sorted_list = sorted(lists, key=itemgetter(1), reverse=True) print(sorted_list) # Output: # [[2500, 'Spark'], [3000, 'Python'], [1000, 'Java'], [2200, 'Hadoop']] 

3. Using lambda along with sorted()

You can also sort a list of lists using lambda expressions along with the sorted() method. To sort by the first element using the lambda expression x[0] for key argument. For example, the key argument is a lambda function that returns the first element of each sublist, which is used as the sorting key . The sorted() function returns a new list with the elements sorted in ascending order based on the sorting key.

 # Sort a list of lists Using lambda expression along with the sorted() lists = [[1000, 'Java'], [2500, 'Spark'], [2200, 'Hadoop'], [3000, 'Python']] sorted_list = sorted(lists, key=lambda x:x[0]) print(sorted_list) # Output: # [[1000, 'Java'], [2200, 'Hadoop'], [2500, 'Spark'], [3000, 'Python']] # Sort a list of lists using lambda along with sorted() method sorted_list = sorted(lists, key=lambda x:x[1]) print(sorted_list) # Output: # [[2200, 'Hadoop'], [1000, 'Java'], [3000, 'Python'], [2500, 'Spark']] 

You can sort a list of lists in descending order by the second element by using the reverse parameter of the sorted() function to specify the index to sort by using the key parameter. For example, the reverse parameter is set to True to sort the list in descending order, and the key parameter is set to lambda x:x[1] to sort by the second element of each list (index 1).

 # Sorted list of lists in descending sorted_list = sorted(lists, key=lambda x: x[1], reverse=True) print(sorted_list) # Output # [[2500, 'Spark'], [3000, 'Python'], [1000, 'Java'], [2200, 'Hadoop']] 

4. Sort a List of Lists Using sort() Method

Alternatively, to sort a list of lists in ascending order, you can also use the sort() method on the list object. By default, the sort() method sorts the elements of a list in ascending order.

 # Sort a list of lists using sort() function lists = [[93, 6], [72, 9], [35, 2]] lists.sort() print(lists) # Output: # [[35, 2], [72, 9], [93, 6]] 

To sort in descending order, use the sort() method with the reverse argument set its value to reverse=True .

 # Sort list of lists in descending order lists.sort(reverse=True) print(lists) # Output # [[93, 6], [72, 9], [35, 2]] 

The key argument in the sort() method can be used to specify a custom sorting key , in this case the length of the inner lists. The len function is used as the key argument to sort the list of lists according to the length of the inner lists.

 # Sort list of lists in key=len lists = [[3, 4, 5], [1, 2], [6, 7, 8, 9]] lists.sort(key=len) print(lists) # Output: # [[1, 2], [3, 4, 5], [6, 7, 8, 9]] 

Conclusion

In this article, I have explained how to sort the list of lists in python by using itemgetter() , sort() , and built-in sorted() function with examples. By using these you can sort the list of lists in ascending order. To sort in descending order, use reverse=True argument.

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References

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Sort a List of Lists in Python

1. Use the itemgetter() Function From the Operator Module Along With the sorted() Function to Sort a List of Lists in Python
2. Use the lambda Expression Along With the sorted() Function to Sort a List of Lists in Python
3. Use the sort() Function to Sort a List of Lists in Python

A list is one of the most powerful data structures used in Python. We can sort a list in Python by arranging all its elements in ascending or descending order based on the requirement.

We can also have nested lists in Python. These can be thought of as a list of lists. Sorting a list of lists arranges all the inner lists according to the specified index as the key.

In this tutorial, we will sort a list of lists in Python based on some indexes.

Use the itemgetter() Function From the Operator Module Along With the sorted() Function to Sort a List of Lists in Python

The function sorted() is used to sort a list in Python. By default, it sorts the list in ascending order. The function itemgetter() from the operator module takes an index number as a parameter and returns the element from the data set placed at that index number.

Therefore, the function sorted(List_name, key=itemgetter(index_number)) sorts a list of lists by the element positioned at the specified index_number of each inner list.

from operator import itemgetter A = [[10, 8], [90, 2], [45, 6]] print("Sorted List A based on index 0: % s" % (sorted(A, key=itemgetter(0)))) B = [[50, 'Yes'], [20, 'No'], [100, 'Maybe']] print("Sorted List B based on index 1: % s" % (sorted(B, key=itemgetter(1)))) 

Sorted List A based on index 0: [[10, 8], [45, 6], [90, 2]] Sorted List B based on index 1: [[100, 'Maybe'], [20, 'No'], [50, 'Yes']] 

To sort a list of lists in descending order, the reverse parameter is used along with the key parameter, and the list name in the sorted() function.

from operator import itemgetter C = [[10, 8, 'Cat'], [90, 2, 'Dog'], [45, 6, 'Bird']] print("Reversed sorted List C based on index 1: % s" % (sorted(C, key=itemgetter(1), reverse=True))) 

Reverse sorted List C based on index 1: [[10, 8, 'Cat'], [45, 6, 'Bird'], [90, 2, 'Dog']] 

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