Is there an R function for comparing rows in data.frame?

Question

I summarized dataset and want to compare the rows with conditions. What functions can I use?

The dataset is from gapminder and I filtered it with two continents. Now I want to compare those rows by total_pop column and want to know in which year Africa has more total population than Europe. But I have no idea which functions can I use.

data <- gapminder %>% 
  filter(continent %in% c("Africa", "Europe")) %>% 
  group_by(continent, year) %>% 
  summarise(total_pop = sum(pop))

I expect the output of 1987, 1992, 1997, 2002, 2007

Answer 1

Since we have same number of rows for "Africa" and "Europe" we can do

unique(data$year[data$total_pop[data$continent == "Africa"] > 
       data$total_pop[data$continent == "Europe"]])
#[1] 1987 1992 1997 2002 2007

Or explicitly doing

Africa_data <- data[data$continent == "Africa",]
Europe_data <- data[data$continent == "Europe",]
Africa_data$year[Africa_data$total_pop > Europe_data$total_pop]
#[1] 1987 1992 1997 2002 2007