Python: Sort one list based on another list containing the desired indexes

Last update on April 19 2025 13:01:11 (UTC/GMT +8 hours)

Sort List by Another List

Write a Python program to sort one list based on another list containing the desired indexes.

Use zip() and sorted() to combine and sort the two lists, based on the values of indexes.
Use a list comprehension to get the first element of each pair from the result
Use the reverse parameter in sorted() to sort the dictionary in reverse order, based on the third argument

Sample Solution:

Python Code:

# Define a function called 'sort_by_indexes' that sorts a list based on a list of corresponding indexes.
def sort_by_indexes(lst, indexes, reverse=False):
    # Use the 'sorted' function to sort the list 'lst' based on the corresponding indexes.
    # The 'zip' function is used to pair each element of 'indexes' with the elements of 'lst'.
    # The sorting is done based on the indexes, and the 'reverse' flag determines whether to sort in reverse order.
    return [val for (_, val) in sorted(zip(indexes, lst), key=lambda x: x[0], reverse=reverse)]

# Example usage: Sort 'l1' based on the corresponding indexes in 'l2'.
l1 = ['eggs', 'bread', 'oranges', 'jam', 'apples', 'milk']
l2 = [3, 2, 6, 4, 1, 5]
print(sort_by_indexes(l1, l2))  # Sort in ascending order.
print(sort_by_indexes(l1, l2, True))  # Sort in descending order.

Sample Output:

['apples', 'bread', 'eggs', 'jam', 'milk', 'oranges']
['oranges', 'milk', 'jam', 'eggs', 'bread', 'apples']

Flowchart:

For more Practice: Solve these Related Problems:

Write a Python program to reorder one list based on the sorted order of a second list.
Write a Python program to sort a list of tuples by matching them with indices from another list.
Write a Python program to sort a list using a custom order provided by a reference list.
Write a Python program to rearrange a list based on a mapping of indices provided by another list.

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