Get minimum unique tuple pair from list of tuples

Question

Consider the following list of tuples:

transactions = [
    ('GBP.USD', '2022-04-29'),
    ('SNOW', '2022-04-26'),
    ('SHOP', '2022-04-21'),
    ('GBP.USD', '2022-04-27'),
    ('MSFT', '2022-04-11'),
    ('MSFT', '2022-04-21'),
    ('SHOP', '2022-04-25')
]

I can get the tuple with the minimum date like this:

min(transactions, key=lambda x: x[1])

This returns a single tuple:

('MSFT', '2022-04-11')

I need to return the minimum date of any duplicates along with all unique values. So my output should be this:

[
    ('SNOW', '2022-04-26'),
    ('SHOP', '2022-04-21'),
    ('GBP.USD', '2022-04-27'),
    ('MSFT', '2022-04-11'),
]

How can I do this?

Answer 1

Solution 1:

min_dates = {}
for item in transactions:
    key, date = item
    if key not in min_dates or date < min_dates[key]:
        min_dates[key] = date
result = [(key, min_dates[key]) for key in min_dates]
result.sort(key=lambda x: x[1])

Solution 2:

from itertools import groupby
# Sort transactions by key and then by date
sorted_transactions = sorted(transactions)

# Group transactions by key
grouped_transactions = groupby(sorted_transactions, key=lambda x: x[0])

# Construct final list of tuples with the minimum date for each key
result = [(key, min(group, key=lambda x: x[1])[1]) for key, group in grouped_transactions]

#print(result)
# Prints : [('GBP.USD', '2022-04-27'), ('MSFT', '2022-04-11'), ('SHOP', '2022-04-21'), ('SNOW', '2022-04-26')]