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# Orderly Set 5.2.3
Orderly Set is a package containing multiple implementations of Ordered
Set.
## OrderlySet
This implementation keeps the order in all set operations except set
difference operations.
As a result, it can do set difference operations much faster than other
implementations. Still 2X slower than of Python's built-in set.
## StableSet
A StableSet is a mutable set that remembers its insertion order.
Featuring: Fast O(1) insertion, deletion, iteration and membership testing.
But slow O(N) Index Lookup.
## StableSetEq
Same as StableSet but the order of items doesn't matter for equality
comparisons.
## OrderedSet
An OrderedSet is a mutable data structure that is a hybrid of a list and a
set.
It remembers its insertion order so that every entry has an index that can
be looked up.
Featuring: O(1) Index lookup, insertion, iteration and membership testing.
But slow O(N) Deletion.
## SortedSet
SortedSet is basically set but when printed, turned into string, or
iterated over, returns the items in alphabetical order.
# Installation
`pip install orderly-set`
# Usage examples
An OrderedSet is created and used like a set:
>>> from orderly_set import OrderedSet
>>> letters = OrderedSet('abracadabra')
>>> letters
OrderedSet(['a', 'b', 'r', 'c', 'd'])
>>> 'r' in letters
True
It is efficient to find the index of an entry in an OrderedSet, or find an
entry by its index. To help with this use case, the `.add()` method returns
the index of the added item, whether it was already in the set or not.
>>> letters.index('r')
2
>>> letters[2]
'r'
>>> letters.add('r')
2
>>> letters.add('x')
5
OrderedSets implement the union (`|`), intersection (`&`), and difference
(`-`)
operators like sets do.
>>> letters |= OrderedSet('shazam')
>>> letters
OrderedSet(['a', 'b', 'r', 'c', 'd', 'x', 's', 'h', 'z', 'm'])
>>> letters & set('aeiou')
OrderedSet(['a'])
>>> letters -= 'abcd'
>>> letters
OrderedSet(['r', 'x', 's', 'h', 'z', 'm'])
The `__getitem__()` and `index()` methods have been extended to accept any
iterable except a string, returning a list, to perform NumPy-like "fancy
indexing".
>>> letters = OrderedSet('abracadabra')
>>> letters[[0, 2, 3]]
['a', 'r', 'c']
>>> letters.index(['a', 'r', 'c'])
[0, 2, 3]
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