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Python sorted() Function

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Index

  1. Definition
  2. Syntax
  3. Parameter Values (input)
  4. Return Values
  5. key Parameter in Python sorted() function
  6. Examples:

Definition

The sorted() function sorts the elements of a given [[Python Iterators, iter and next|iterable]] in a specific order (ascending or descending) and returns it as a list.

Syntax

sorted(iterable, key=None, reverse=False)

Parameter Values (input)

ParameterDescription
iterableIterator objects that will be joined together
reverse (Optional)If True, the sorted list is reversed (or sorted in descending order). Defaults to False if not provided.
key (Optional)A function that serves as a key for the sort comparison. Defaults to None.

Recommended Reading: [[Python Iterators, iter and next]]

Return Values

oss:

  • sorted() returns always a list independently of the input type

Example 1) Sort string, list, and tuple;

# vowels list
py_list = ['e', 'a', 'u', 'o', 'i']
print(sorted(py_list)) 
# Output: ['a', 'e', 'i', 'o', 'u']
 
# string
py_string = 'Python'
print(sorted(py_string)) 
# Output: ['P', 'h', 'n', 'o', 't', 'y']
 
 
# vowels tuple
py_tuple = ('e', 'a', 'u', 'o', 'i') 
# Output: ['a', 'e', 'i', 'o', 'u']
 
print(sorted(py_tuple))

Example 2) Sort in descending order:

The sorted() function accepts a reverse parameter as an optional argument.

Setting reverse = True sorts the iterable in the descending order.

# set
py_set = {'e', 'a', 'u', 'o', 'i'}
print(sorted(py_set, reverse=True))
# Output: ['u', 'o', 'i', 'e', 'a']
 
# dictionary
py_dict = {'e': 1, 'a': 2, 'u': 3, 'o': 4, 'i': 5}
print(sorted(py_dict, reverse=True))
# Output: ['u', 'o', 'i', 'e', 'a']
 
# frozen set
frozen_set = frozenset(('e', 'a', 'u', 'o', 'i'))
print(sorted(frozen_set, reverse=True))
# Output: ['u', 'o', 'i', 'e', 'a']

Key Parameter in Python sorted() function

If you want your own implementation for sorting, sorted() also accepts a key function as an optional parameter.

Based on the returned value of the key function, you can sort the given iterable.

Example 1:

sorted(iterable, key=len)

Here, len() is Python’s in-built function to count the length of an object. The list is sorted based on the length of the element, from the lowest count to highest.

Example2:

# take the second element for sort
def take_second(elem):
    return elem[1]
 
 
# random list
random = [(2, 2), (3, 4), (4, 1), (1, 3)]
 
# sort list with key
sorted_list = sorted(random, key=take_second)
 
# print list
print('Sorted list:', sorted_list)
# Output: Sorted list: [(4, 1), (2, 2), (1, 3), (3, 4)]

Examples:

Sorting a dict by the values

oss: Usually a dict i sorted by the key

py_dict = {'a': 5, 'e': 4, 'i': 3, 'o': 2, 'u': 1}
print(sorted(py_dict, key = lambda x: py_dict.get(x)))
# Output: ['u', 'o', 'i', 'e', 'a']

Sorting agenda by specific info

agenda =[ 
		  {'nome':'Paperino','cognome':'Paolino', 'phone':'555-1313', 'city':'Paperopoli'},
		  {'nome':'Gastone', 'cognome':'Paperone', 'telefono':'555-1717', 'città':'Paperopoli'},
		  {'nome': 'Archimede','cognome':'Pitagorico','telefono':'555-11235', 'città': 'Paperopoli'}
		]
 
print(agenda_sorted = sorted(agenda, key=lambda diz: (diz['cognome'])))
 
#Output: [{'nome': 'Paperino', 'cognome': 'Paolino', 'phone': '555-1313', 'city': 'Paperopoli'}, 
#         {'nome': 'Gastone', 'cognome': 'Paperone', 'telefono': '555-1717', 'città': 'Paperopoli'}, 
#         {'nome': 'Archimede', 'cognome': 'Pitagorico', 'telefono': '555-11235', 'città': 'Paperopoli'}]

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