merge playlist.py

import random

# Merges rated songs with new songs while preferring more recent songs

""" Example output

5 new songs
9 rated songs

Weights: [1.0, 0.5, 0.333 ... 0.143, 0.125, 0.111]

Picked 2 rated songs:
['2', '7']

New list:
['2', '1', '2', '7', '3', '4', '5']

7 song ids saved to 'new list.txt'

"""

with open("new song ids.txt") as f:
    new_song_ids = f.read().splitlines()

with open("rated songs.txt") as f:
    # Most recent first
    rated_song_ids = f.read().splitlines()

save_file = "new list.txt"

ratio = 2
# The ratio of new songs compared to rated songs
# Ratio 0.5 is 2 rated songs for every new song, songlist size is tripled.
# Ratio 1 corresponds to equal mix with a doubled songlist size.
# Ratio 4 songlist size is 1.25 of the original.

number_of_songs_to_pick = int(len(new_song_ids) / ratio)
assert number_of_songs_to_pick <= len(rated_song_ids)


def insert_elements_at_nth_index(lst, elements, n):
    whole_part = int(n)
    fractional_part = n - whole_part
    index = 0
    for element in elements:
        lst.insert(int(index), element)
        index += whole_part + 1
        index += fractional_part
    return lst


def random_with_priority_no_duplicates(lst, num_items, offset=0):
    selected_indices = []
    available_indices = list(range(len(lst)))
    initial_weights = [
        round((1 + offset) / (i + 1 + offset), 3) for i in available_indices
    ]
    print(
        f"\nWeights: {str(initial_weights[:3])[:-1]} ... {str(initial_weights[-3:])[1:]}"
    )

    for _ in range(num_items):
        weights = [(1 + offset) / (i + 1 + offset) for i in available_indices]
        index = random.choices(available_indices, weights=weights, k=1)[0]
        selected_indices.append(index)
        available_indices.remove(index)

    selected_items = [lst[i] for i in selected_indices]
    return selected_items


print(f"{len(new_song_ids)} new songs")
print(f"{len(rated_song_ids)} rated songs")


offset = len(rated_song_ids) // 10
selected_items = random_with_priority_no_duplicates(
    rated_song_ids, number_of_songs_to_pick, offset=int(offset)
)

print(f"\nPicked {number_of_songs_to_pick} rated songs:")
print(selected_items)

new_list = insert_elements_at_nth_index(new_song_ids, selected_items, ratio)
print("\nNew list:")
print(new_list)

with open(save_file, "w") as f:
    f.write("\n".join(new_list))

print(f"\n{len(new_list)} song ids saved to '{save_file}'")