Python- Accessing lists in dictionaries

Question

So, I am trying to solve this problem where I have to return a dictionary of all people who went on dates.

For example, this input:

[
    ["john", "amy"],
    ["abby", "john"],
    ["john", "michael"],
    ["michael", "chris"],
]

Should output:

{
    "john": set(["amy", "abby", "michael"]),
    "amy": set(["john"]),
    "abby": set(["john"]),
    "michael": set(["john", "chris"]),
    "chris": set(["michael"]),
}

but I have no idea how I can save the names and then insert it into a dictionary. I've tried looping through the list twice, but no luck.

Below, is the function that I've been using to return the necessary dictionary.

def return_all_dates(people_who_went_on_dates):
    pass

Do you know how to create an empty dictionary? How to add an entry to a dictionary? How to add an item to a set? — Scott Hunter
– Scott Hunter, Commented Jun 22, 2021 at 5:52

Ferid Heziyev · Accepted Answer · 2021-06-22 06:00:31Z

1

you can do it like this:

dates = dict()

for row in people_who_went_on_dates:
    person1, person2 = row
    if person1 not in dates:
        dates[person1] = set()
    if person2 not in dates:
        dates[person2] = set()
    dates[person1].add(person2)
    dates[person2].add(person1)

answered Jun 22, 2021 at 6:00

Ferid Heziyev

3202 silver badges13 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Алексей Р Over a year ago

can be simplified using dates.setdefault(row[0], set()).add(row[1])

AgnesM · Accepted Answer · 2021-06-22 08:00:20Z

Here is my approach:

data = [
    ["john", "amy"],
    ["abby", "john"],
    ["john", "michael"],
    ["michael", "chris"],
]

def return_dates(all_dates):

    #Create empty dictionary
    dates = {}

    #Iterate over each date
    for date in all_dates:

        #Add first person if not exists in the dictionary
        if date[0] not in dates:

            #Assign value with a list of 1 element
            dates[date[0]] = [date[1]]

        #Add second person too if not exists too
        if date[1] not in dates:

            #Assign value with a list of 1 element
            dates[date[1]] = [date[0]]
        
        #if one or both persons exists in the dictionary, we do different steps
        #Add second person to the first person list only if it does not exists
        if date[1] not in dates[date[0]]:

            #List method append to add a new element
            dates[date[0]].append(date[1])

        #Add first person to the second person list only if it does not exists
        if date[0] not in dates[date[1]]:

            dates[date[1]].append(date[0])  
    
    #return dictionary
    return dates
            
result = return_dates(data)

print(result)

{'john': ['amy', 'abby', 'michael'], 'amy': ['john'], 'abby': ['john'], 'michael': ['john', 'chris'], 'chris': ['michael']}

Collectives™ on Stack Overflow

Python- Accessing lists in dictionaries

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related