如何在R中应用多个if语句？

问题描述

我有一个数据框（df），其中列出了与每个网站相关联的国家/地区

I have a data frame (df) that lists the countries associated with every site

Site          Country
Site1         USA
Site2         Vietnam
Site3         Spain
Site4         Germany
Site5         China

我想附上一个专栏，每个国家都与其相应的大陆相关联。我写了一个简单的 if loop 来做这件事：

I want to attach a column, where for each country I associate its corresponding continent. I wrote a simple if loop to do this:

df$Continent <- NA
if(df$Country == "USA" |df$Country ==  "Canada" |df$Country == "Mexico")
 {df$Continent <- "North America"}
if(df$Country == "Spain" |df$Country == "France" |df$Country == "Germany")
{df$Continent <- "Europe"}
## .. etc

summary(df)

但是，每当我运行df时，我发现它将北美分配给所有国家。我知道这可能听起来微不足道，但是如果我使用 if 各地的法规而不是 else 或者 if else ？有任何纠正这个的建议吗？

However, each time I run it the df, I find that it assigns North America to all the countries. I understand that this may sound trivial, but does it make a difference if I use if statments everywhere and not else or if else? Any suggestions for correcting this?

推荐答案

我喜欢 ifelse（） for像这样的事情。您可以将它与％in％运算符一起使用，如下所示：

I like ifelse() for things like this. You could use it with the %in% operator like this:

df$Continent <- ifelse(df$Country %in% c("USA", "Canada", "Mexico"),
                       "North America", df$Continent)
df$Continent <- ifelse(df$Country %in% c("Spain", "France", "Germany"),
                       "Europe", df$Continent)
df
   Site Country     Continent
1 Site1     USA North America
2 Site2 Vietnam          <NA>
3 Site3   Spain        Europe
4 Site4 Germany        Europe
5 Site5   China          <NA>

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