Store Different Types of Values in One Key - Dictionary

Question

I want to make a "travel" summary that looks like:

There are 4 starting points to reach Chicago . To access this city, you can use: Highway X, Highway Z, Highway ZZ.

The data that I currently have looks something like:

Highway X, NY, Chicago

Highway Z, LA, Chicago

Highway X, Austin, Chicago

Highway ZZ, Miami, Chicago

My question: What should I use to store these data properly?

I tried to use a dictionary with a list inside of it. However, it didn't work because I couldn't store the list of Highway. I only managed to get something like

{Chicago: [NY, LA, Austin]}

UPDATE!!

I just figured out that there's duplication in my data, and that's not a good news because I want the starting points to be distinct. Right now it looks like this:

Highway X, NY, Chicago

Highway X, NY, Chicago

Highway Z, LA, Chicago

Highway X, Austin, Chicago

Highway ZZ, Miami, Chicago

Highway X, NY, Chicago

Answer 1

The best way of organising your data depends on what you want to do with them.

Do you want to answer questions like "I'm in Austin, which Highway do I have to take to get to Chicago?"

Then your keys should be the departure cities:

lookup = {'Austin': 'Highway X',
          'NY': 'Highway X',
          'LA': 'Highway Z',
          'Miami': 'Highway ZZ'}

Because then you can answer the question by simply looking up the asker's starting point:

lookup['Austin']
# prints
# Highway X

But if you want to answer different questions like "Someone travelling on Highway X which city are they more likely to come from?" then you'd organise your data differently.

If you just want to print them, use a 'lil' (list of lists)

table = [["Highway X", "NY", "Chicago"],
         ["Highway Z", "LA", "Chicago"],
         ["Highway X", "Austin", "Chicago"],
         ["Highway ZZ", "Miami", "Chicago"]]

Then you can easily format

for row in table:
    print("{:12}{:8}{:10}".format(*row))

Answer 2

Use a list of tuples in your dictionary. The first item in each tuple would be the highway, the second the starting point.

routes = {'Chicago': [('Highway X', 'NY'), ('Highway Z', 'LA'), ('Highway AX', 'Austin'), ('Highway ZZ', 'Miami')]}

Then it's trivial to produce the summary:

for city in routes:
    paths = ', '.join(sorted({route[0] for route in routes[city]}))
    print("There are {} starting points to reach {}. To access this city, you can use: {}".format(len(routes[city]), city, paths))

The first line uses a set comprehension to remove duplicate highways and then sorts and joins them to make a string. That string as well as the destination city and number of routes is then used to construct the final summary string. The output of the above code would be:

There are 4 starting points to reach Chicago. To access this city, you can use: Highway X, Highway Z, Highway ZZ

---

An easy way to construct the routes dict is to use a collections.defaultdict of lists. Assuming that your data is coming from a CSV file:

import csv
from collections import defaultdict

routes = defaultdict(list)

with open('data.csv') as f:
    reader = csv.reader(f)
    for highway, start, dest in reader:
        routes[dest].append((highway, start))

Answer 3

Nest some dictionaries. This allows you to follow a "route."

{'Highway X': {'Austin': 'Chicago', 'NY': 'Chicago'},
 'Highway Z': {'LA': 'Chicago'},
 'Highway ZZ': {'Miami': 'Chicago'}}

Alternatively:

{'Austin': {'Highway X': 'Chicago'},
 'LA': {'Highway Z': 'Chicago'},
 'Miami': {'Highway ZZ': 'Chicago'},
 'NY': {'Highway X': 'Chicago'}}