Python sorted containers

Sorted Containers is a powerful Python library that provides fast and easy-to-use implementations of SortedList, SortedDict and SortedSet data types. Unlike Python’s built-in types, these containers maintain their elements in sorted order automatically as elements are added or removed. To use this library, you need to install it using the following command:

pip install sortedcontainers

Why use sorted containers?

Let's understand the use cases of Sorted Containers.

• Automatic Sorting: Keeps your data sorted automatically without needing to call sort() every time you update it.
• Fast and Efficient: Written in Python but optimized for speed, often matching C-based libraries.
• Easy to Use: Works just like Python's list, dict and set, so it's easy to learn and use.
• Memory Efficient: Uses advanced structures like B-trees to balance speed and memory usage effectively.

Key components of sorted containers

Let’s understand the key components of the sortedcontainers library, which automatically maintain sorted order while offering efficient and intuitive operations.

1. SortedList: It is a special type of list from the sortedcontainers module. It automatically maintains the order of its elements, meaning that each time you add or remove an element, the list remains sorted. Its key functions include:

• add(value) inserts the value while maintaining order.
• update(iterable) adds all values from an iterable, maintaining order.
• clear() removes all elements.
• discard(value) removes the value if it exists.

from sortedcontainers import SortedList

a = SortedList([1, 2, 3, 4, 5])
print(a)

a.add(6)
print(a)

a.clear()
print(a)

Output

SortedList([1, 2, 3, 4, 5])
SortedList([1, 2, 3, 4, 5, 6])
SortedList([])

Explanation:

• SortedList([1, 2, 3, 4, 5]) initializes a sorted list and a.add(6) inserts 6 while maintaining the sorted order.
• a.clear() removes all elements from the list, making it an empty SortedList([]).

2. SortedSet: It is a mutable set that maintains unique elements in sorted order. It combines set operations with sorting. It's key functions include:

• add(value) adds a value while maintaining order.
• clear() removes all elements.
• discard(value) removes the value if it exists.

from sortedcontainers import SortedSet

a = SortedSet([1, 2, 3, 4, 5])
print(a)

a.add(6)
print(a)

a.discard(3)
print(a)

Output

SortedSet([1, 2, 3, 4, 5])
SortedSet([1, 2, 3, 4, 5, 6])
SortedSet([1, 2, 4, 5, 6])

Explanation:

• SortedSet([1, 2, 3, 4, 5]) initializes a sorted set with unique elements and a.add(6) inserts 6 while maintaining the sorted order.
• a.discard() removes the value 3 from the set if it exists.

3.SortedDict: It is a mutable mapping that maintains keys in sorted order. It combines dictionary functionality with sorting. It's key functions include:

• setdefault(key, default) returns the value for the key, inserting the key with a default if not found.
• clear() removes all key-value pairs.
• get(key, default) retrieves the value for the key or the default if not present.

from sortedcontainers import SortedDict

d = SortedDict({3: 'c', 1: 'a', 2: 'b'})
print(d)

d[0] = 'z'
print(d)

val = d.setdefault(4, 'd')
print(d)
print(val)

miss = d.get(5, 'default_value')
print(miss)

d.clear()
print(d)

Output

SortedDict({1: 'a', 2: 'b', 3: 'c'})
SortedDict({0: 'z', 1: 'a', 2: 'b', 3: 'c'})
SortedDict({0: 'z', 1: 'a', 2: 'b', 3: 'c', 4: 'd'})
d
default_value
SortedDict({})

Explanation:

• SortedDict({3: 'c', 1: 'a', 2: 'b'}) initializes a dictionary and automatically sorts keys.
• a[0] = 'z' adds a new key-value pair, the dictionary is re-sorted as {0, 1, 2, 3}.
• a.setdefault(4, 'd') checks if key 4 exists if not, adds it with value 'd'.
• a.get(5, 'default_value') tries to get value for key 5 and returns the default since 5 doesn't exist.
• a.clear() removes all items from the dictionary.