我正在尝试用R做一些代码分析，但遇到了一个问题。实际上，我使用的是“人口数据”，我想根据地区对国家进行排序（大洋洲、亚洲、欧洲......等等）。为此，我需要使用一个条件结构来检查一个国家是否在某个地区。尽管如此，我无法对多个地区（两个以上）执行此操作。
作为第一个解决方案，我尝试用if，else if，else来构造条件结构：

if(population_df$country %in% europe_countries) {
  population_df$region <- "Europe"
}
else if(population_df$country %in% africa_countries) {
  population_df$region <- "Africa"
}
else if(population_df$country %in% america_countries) {
  population_df$region <- "America"
}
else if(population_df$country %in% oceania_countries) {
  population_df$region <- "Oceania"
}
else if(population_df$country %in% asia_countries) {
  population_df$region <- "Asia"
}

但它不起作用，因为控制台加载错误如下：
如果（% europe_countries中的population_df$country %）{：条件的长度大于1
通过在网页上搜索，我理解了这个错误，因为我不能在if结构中使用向量（我不知道为什么，但这是事实）。
我用if_else结构尝试了第二种解决方案：

population_df$region <- if_else(population_df$country %in% europe_countries, "Europe", "")
population_df$region <- if_else(population_df$country %in% africa_countries, "Africa", "")

但正如所料，它不起作用，因为如果我有一个欧洲国家，我的第二个if_else将用“"替换“Europe”。
我没有其他办法让我的剧本运作起来，所以如果你们中的任何人有一个想法，那将是一种荣幸。
这里我的完整代码：

library(tidyverse)
library(ggplot2)

View(population)

spe_countries <- c("Nigeria", "Egypt", "Ethiopia", "France", "Germany", "Spain", "United States of America",
                   "Canada", "Mexico", "Australia", "New Zealand", "China", "Japan", "India")

europe_countries <- c("France", "Germany", "Spain")
africa_countries <- c("Nigeria", "Egypt", "Ethiopia")
america_countries <- c("United States of America","Canada", "Mexico")
oceania_countries <- c("Australia", "New Zealand")
asia_countries <- c("China", "Japan", "India")

population_df <- population %>%
  filter(country %in% spe_countries)

View(population_df)

if(population_df$country %in% europe_countries) {
  population_df$region <- "Europe"
}
else if(population_df$country %in% africa_countries) {
  population_df$region <- "Africa"
}
else if(population_df$country %in% america_countries) {
  population_df$region <- "America"
}
else if(population_df$country %in% oceania_countries) {
  population_df$region <- "Oceania"
}
else if(population_df$country %in% asia_countries) {
  population_df$region <- "Asia"
}

population_df$region <- if_else(population_df$country %in% europe_countries, "Europe", "")
population_df$region <- if_else(population_df$country %in% africa_countries, "Africa", "")