Count how many people are alive per year, based on their birthyear and deathyear, aims for performances.

count_living_per_year_perf.py

import collections
import random
import timeit

pop = [
    (b := random.randint(1900, 2000), random.randint(b + 1, b + 100))
    for _ in range(10000)
]


# 0.162 s (with 10000 people [1,100] years old)
def count_living_per_year(population: list[tuple[int, int]]) -> dict[int, int]:
    living_per_year = {}
    for birth, death in population:
        if birth in living_per_year:
            living_per_year[birth] += 1
        else:
            living_per_year[birth] = 1
        if death in living_per_year:
            living_per_year[death] -= 1
        else:
            living_per_year[death] = -1
    for year in range(min(living_per_year), max(living_per_year)):
        living_per_year[year] += living_per_year.get(year - 1, 0)
    living_per_year.pop(max(living_per_year))
    return living_per_year


print(sorted(tuple(count_living_per_year(pop).items())))
print(
    timeit.timeit(
        "count_living_per_year(pop)",
        globals=globals(),
        number=100,
    )
)


# 0.118 s (with 10000 people [1,100] years old)
def count_living_per_year(population: list[tuple[int, int]]) -> dict[int, int]:
    living_per_year = collections.defaultdict(int)
    for birth, death in population:
        living_per_year[birth] += 1
        living_per_year[death] -= 1
    min_, max_ = min(living_per_year), max(living_per_year)
    for year in range(min_, max_):
        living_per_year[year] += living_per_year[year - 1]
    del living_per_year[min_ - 1], living_per_year[max_]
    return living_per_year


print(sorted(tuple(count_living_per_year(pop).items())))
print(
    timeit.timeit(
        "count_living_per_year(pop)",
        globals=globals(),
        number=100,
    )
)


# 0.105 s (with 10000 people [1,100] years old)
def count_living_per_year(population: list[tuple[int, int]]) -> dict[int, int]:
    births = collections.Counter(birth for birth, _ in population)
    deaths = collections.Counter(death for _, death in population)
    living_per_year = births
    for year in range(min(births), max(deaths)):
        living_per_year[year] += living_per_year[year - 1] - deaths[year]
    return living_per_year


print(sorted(tuple(count_living_per_year(pop).items())))
print(
    timeit.timeit(
        "count_living_per_year(pop)",
        globals=globals(),
        number=100,
    )
)


# 0.108 s (with 10000 people [1,100] years old)
def count_living_per_year(population: list[tuple[int, int]]) -> dict[int, int]:
    births = collections.Counter(birth for birth, _ in population)
    deaths = collections.Counter(death for _, death in population)
    (delta_per_year := births).subtract(deaths)
    living_per_year = collections.Counter()
    for year in range(min(delta_per_year), max(delta_per_year)):
        living_per_year[year] = living_per_year[year - 1] + delta_per_year[year]
    return living_per_year


print(sorted(tuple(count_living_per_year(pop).items())))
print(
    timeit.timeit(
        "count_living_per_year(pop)",
        globals=globals(),
        number=100,
    )
)


# 0.093 s (with 10000 people [1,100] years old)
def count_living_per_year(population: list[tuple[int, int]]) -> dict[int, int]:
    births, deaths = zip(*population)
    births_counter = collections.Counter(births)
    deaths_counter = collections.Counter(deaths)
    living_per_year = collections.Counter()
    for year in range(min(births_counter), max(deaths_counter)):
        delta_living = births_counter[year] - deaths_counter[year]
        living_per_year[year] = living_per_year[year - 1] + delta_living
    return living_per_year


print(sorted(tuple(count_living_per_year(pop).items())))
print(
    timeit.timeit(
        "count_living_per_year(pop)",
        globals=globals(),
        number=100,
    )
)