Specification: Find the name of the continent with the highest average population by country.
Example input/output:
Input: `countries`
namepopulationcontinent
`USA``328``North America`
`Canada``37``North America`
`Ethiopia``109``Africa`
`Kenya``51``Africa`
Output: `North America`

### Python - Imperative

```def continent_by_population(countries):
continent_stats = defaultdict(lambda: [0, 0])
for country in countries:
continent = country['continent']
continent_stats[continent] += country['population']
continent_stats[continent] += 1

max_continent = None
max_average = None
for continent, [total, count] in continent_stats.items():
average = total / count
if max_average is None or max_average < average:
max_average = average
max_continent = continent

return max_continent```

### Python - Functional

```def continent_by_population(countries):
continents = set([c['continent'] for c in countries])
populations_by_continent = [
(continent, [c['population'] for c in countries
if c['continent'] == continent])
for continent in continents
]
averages = [
(continent, sum(pops) / len(pops))
for continent, pops in populations_by_continent
]
return max(averages, key=lambda t: t)```

### Python - Pandas

```def continent_by_population(countries):
mean_pop = countries.groupby('continent').population.mean()
return mean_pop.index[mean_pop.argmax()]```

### R - Tidyverse

```continent_by_population <- function(countries) {
countries %>%
group_by(continent) %>%
summarize(mean_pop = mean(population)) %>%
slice(which.max(mean_pop)) %>%
.\$continent
}```

### SQL - SQLite

```SELECT continent
FROM countries
GROUP BY continent
ORDER BY AVG(population) DESC
LIMIT 1```

### Datalog - Souffle

```.decl average_population(Continent:symbol, Avg:number)
average_population(Continent, Avg) :-
countries(Continent, _, _),
Total = sum P : countries(Continent, _, P),
Num_countries = count : countries(Continent, _, _),
Avg = Total / Num_countries.

continent_by_population(Continent) :-
countries(Continent, _, _),
average_population(Continent, Max_avg),
Max_avg = max A : { countries(C, _, _), average_population(C, A) }.```

### Q - kdb+

```averages:
select avg(population) by continent from countries;
continent_by_population:
(first select[>population] continent from averages) `continent```