# SETS

* like dictionaries, but with keys only (no values)
* properties: unordered, iterable, mutable, can contain multiple data types
* made up of unique elements (strings, numbers, or tuples)

## create an empty set
```python
empty_set = set()
```

## create a set
```python
languages = {'python', 'r', 'java'}         # create a set directly
snakes = set(['cobra', 'viper', 'python'])  # create a set from a list
```

## examine a set
```python
len(languages)              # returns 3
'python' in languages       # returns True
```

## set operations
```python
languages & snakes          # returns intersection: {'python'}
languages | snakes          # returns union: {'cobra', 'r', 'java', 'viper', 'python'}
languages - snakes          # returns set difference: {'r', 'java'}
snakes - languages          # returns set difference: {'cobra', 'viper'}
```

## modify a set (does not return the set)
```python
languages.add('sql')        # add a new element
languages.add('r')          # try to add an existing element (ignored, no error)
languages.remove('java')    # remove an element
languages.remove('c')       # try to remove a non-existing element (throws an error)
languages.discard('c')      # removes an element if present, but ignored otherwise
languages.pop()             # removes and returns an arbitrary element
languages.clear()           # removes all elements
languages.update('go', 'spark') # add multiple elements (can also pass a list or set)
```

## get a sorted list of unique elements from a list
```python
sorted(set([9, 0, 2, 1, 0]))    # returns [0, 1, 2, 9]
```


## set comprehension
```python
fruits = ['apple', 'banana', 'cherry']
unique_lengths = {len(fruit) for fruit in fruits}   # {5, 6}
```