List of tuples merging

Question

I am having trouble with lists of tuples inside them.

If I have a list of tuples like this:

list = [('1', 'a'), ('2', 'b'), ('3', 'c'), ('3', 'd'), ('4', 'e'), ('4', 'f'), ('5', 'g')]

but instead I want to have it formatted like this, where there is only one of each number with a list of letters that are following those numbers instead of them being all separate:

list = [('1', ['a']), ('2', ['b']), ('3', ['c', 'd']), ('4', ['e', 'f']), ('5', ['g'])]

what would be the approach?

Answer 1

Create a grouping dictionary where keys are first values from tuple and values are lists. Then you can convert this dictionary to a final list:

lst = [
    ("1", "a"),
    ("2", "b"),
    ("3", "c"),
    ("3", "d"),
    ("4", "e"),
    ("4", "f"),
    ("5", "g"),
]

out = {}
for a, b in lst:
    out.setdefault(a, []).append(b)

out = list(out.items())
print(out)

Prints:

[('1', ['a']), ('2', ['b']), ('3', ['c', 'd']), ('4', ['e', 'f']), ('5', ['g'])]