104 lines
1.7 KiB
Markdown
104 lines
1.7 KiB
Markdown
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---
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tags: [python, data-structures]
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---
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# Sets in Python
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- They are **unordered**
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- You can increase/decrease their length by adding/removing new members
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- They **do not allow duplicate members**
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- **Can only hold immutable objects**
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> Sets are denoted with `{...}`
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## Basic usage
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```python
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basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}
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print(basket) # show that duplicates have been removed
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print(len(basket))
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# {'apple', 'pear', 'banana', 'orange'}
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# 4
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```
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## Looping through sets
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```python
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for item in basket:
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print(item)
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"""
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apple
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pear
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banana
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orange
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"""
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```
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## Check for membership
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```python
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basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}
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print('apple' in basket)
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# True
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```
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## Remove items from set
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> `remove` will raise an error if the specified item does not exist, `discard`
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> will not
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```python
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basket.remove('apple')
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basket.discard('apricot')
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print(basket)
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# {'pear', 'banana', 'orange'}
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basket.clear()
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print(basket)
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#set
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```
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## Add items to a set
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```python
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basket.add('apricot')
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print(basket)
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# {'apricot', 'pear', 'banana', 'orange'}
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```
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## Start with empty set
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To declare an empty set you cannot just do:
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```py
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my_set = {}
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```
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You have to use a constructor:
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```py
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my_set = set()
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```
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## Apply unions and intersections
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```python
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s1 = {'apple', 'orange', 'banana'}
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s2 = {'grapefruit', 'lime', 'banana'}
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print('Union:', s1 | s2)
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# Union: {'apple', 'orange', 'grapefruit', 'lime', 'banana'}
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print('Intersection:', s1 & s2)
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# Intersection: {'banana'}
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print('Difference:', s1 - s2)
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# Difference: {'orange', 'apple'}
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print('Symmetric Difference:', s1 ^ s2)
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#Symmetric Difference: {'apple', 'orange', 'grapefruit', 'lime'}
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```
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