Sets. And ZIP codes?

Transcription

1 Sets And ZIP codes?

2 Set In mathematics, a set is an unordered collection of mutually distinct objects In other words: The elements of a set are in no order All of the elements in the set are different from each other Everything is in the set either zero times or exactly once There is no restriction on what type of objects can be stored in a set

3 Creating sets Sets can only be created using the set function The set function takes zero or one arguments You can pass zero arguments to create an empty set You can pass an iterable to the set function to create a set out of the elements of the iterable

4 Creating Sets

5 Creating Sets

6 Creating Sets

7 Accessing Set Data Sets support many of the things we've seen in sequences so far

8 Accessing Set Data

9 Adding and Removing Elements Sets provide add and remove methods to add and remove elements

10 Adding and Removing Elements Sets provide an update method that adds elements to the set from an iterable

11 Set Operations Mathematically, sets allow a number of options to combine different sets together Python supports many of these operations It can be difficult to conceptually think of how sets work Remember Venn diagrams?

12 Venn Diagrams

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24 A B S

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26 Subsets and Supersets A set X is a subset of Y if and only if every element of X is an element of Y A set X is a superset of Y if and only if every element of Y is an element of X

27 5 9 A B S What is the value of the following expressions? A.issubset(B) B.issubset(A) A.union(S) S.symmetric_difference(D) C.issubset(S) S.intersection(D) len(s) S.difference(A)

28 Zip Codes Zip codes were created by the USPS in order to aid in mail delivery efficiency Each zip code represents a postal route Each zip code has a canonical city and state associated with it A city may have zero, one, or many zip codes associated with it

29 Example: Spokane Zip Codes Spokane, MO has Spokane, WA has 99201, 99202, 99203, 99204, 99205, 99206, 99207, 99208, 99209, 99210, 99211, 99212, 99213, 99214, 99215, 99216, 99217, 99218, 99219, 99220, 99223, 99224, 99228, 99251, 99252, 99256, 99258, 99260, 99299

30 Zip Codes There are freely available datasets that contain information on all of the zip codes in the US (42,523 of them) Many of these datasets are made available in a format referred to as Comma-Separated Values (or CSV) CSVs are record-based files that can be thought of as a humanreadable way to store spreadsheet-style data On Friday, we'll be working with a CSV file storing information on the various zip codes

31 CSV files Each record in a CSV file takes up a single line Within a line, fields are separated by commas For example...

32 Ikea Product Width Depth Height Price Malm Billy Kivik Tarva Product,Width,Depth,Height,Price Malm,31,18,30,89.99 Billy,15,11,79,69.99 Kivik,110,64,32,929 Tarva,18,15,24,39.99

33 Loading in CSV data We want to be able to load in data from a CSV file For the zip code file, we don't want to load the entire file in at once Instead, we want to process this one record at a time, storing only the data we need from each record Suppose we want to find the total volume of these purchases from Ikea... Malm,31,18,30,89.99 Billy,15,11,79,69.99 Kivik,110,64,32,929 Tarva,18,15,24,39.99

34 Poll Time! Take out a sheet of paper, DO NOT PUT YOUR NAME ON IT, and answer the following question: When would you rather have exam 3? Monday, November 23 (the Monday before Thanksgiving) Monday, November 30 (the Monday after Thanksgiving)