Day16

Day 16: Sets

Instructions:

1. Open a new python file.
2. Similar to dictionaries, sets are unordered collections of data. Unlike dictionaries, sets do not contain key/value pairs. A set should be used over a list only if there is no need for the collection to be ordered. Sets are created with curly brackets ({}) or with the set() function. Sets are best used for applications that contain a collection of stop words. The program is able to scan the contents of a set substantially faster than the contents of a list.

   suspects = {"Verbal", "Keaton", "McManus", "Fenster"}
   investigators = set(["Dave Kujan", "Jack Baer", "Jeff Rabin"])
   print(suspects)
   print(investigators)
   

3. Sets are mutable, so items can be added to the collection.

   suspects.add("Hockney")
   print(suspects)
   

4. Sets can be iterated through similar to lists.

   for person in suspects:
    	print("{} was brought in for a line up.".format(person))
   

5. Two sets can be combined using the union() method.

   numbers1 = set([1, 2, 3, 4, 5])
   numbers2 = set([6, 7, 8, 9, 10])
   print(numbers1.union(numbers2))
   

6. The .intersection() method is used to return only the items that matched between two sets.

   evens = set([0, 2, 4, 6, 8])
   nums = set([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
   print(nums.intersection(evens))
   

7. The .difference() method is used to return only the items that don't match between two sets.

   evens = set([0, 2, 4, 6, 8])
   nums = set([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
   print(nums.difference(evens))
   

8. The .difference_update() method is used to update a set by removing items that match another set. The method does not produce an output, but overwrites the primary set instead.

   evens = set([0, 2, 4, 6, 8])
   nums = set([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
   print("Evens: {}".format(nums))
   print("Evens Difference Update: {}".format(nums.difference_update(evens)))
   print("Evens: {}".format(nums))
   

9. The .symmetric_difference() method can be used to return only the unique items in two sets.

   evens = set([0, 2, 4, 6, 8])
   nums = set([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
   print(nums.symmetric_difference(evens))
   

10. The .symmetric_difference_update() method is used to update a set with only the unique items from two sets. The method does not produce an output, but overwrites the primary set instead.

evens = set([0, 2, 4, 6, 8])
nums = set([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
print("Evens: {}".format(nums))
print("Symmetric Difference Update: {}".format(nums.symmetric_difference_update(evens)))
print("Evens: {}".format(nums))

11. Since sets are unsorted, the sorted() function can be used to provide a sorted output.

print(suspects)
print(sorted(suspects))

12. The .discard() and .remove() methods are used to remove the specified item from the set. If the specified item is not in the set, the .remove() method will throw an error, while the .discard() method will not.

evens = set([0, 2, 4, 6, 8])
evens.discard(0)
evens.remove(2)
print(evens)
evens.discard(0)
evens.remove(2)
print(evens)

13. In order to avoid the error while using the .remove() error, the try/except process should be used.

suspects = {"Verbal", "Keaton", "McManus", "Fenster"}
try:
   suspects.remove("Kaiser Soze")
except KeyError:
   print("Kaiser Soze is not one of the usual suspects.")

14. While sets are mutable, the frozenset() function can be used to create immutable sets. None of the update methods will execute on a frozenset().

suspects = frozenset(["Verbal", "Keaton", "McManus", "Fenster"])
suspects.add("Kaiser Soze")
print(suspects)

15. The .clear() method empties the entire set.

print(nums)
nums.clear()
print(nums)

16. For additional information about sets, read this article.
17. Update the log file with what you have learned today.