如何在R语言中合并两列信息新增一列？

原始数据 #

Dat <- c("B", "A", "A", "B", "B")
Nat <- c("B", "B", "A", "B", "A")

df <- data.frame(Nat, Dat)

需求说明 #

根据Nat和Dat的取值组合，新增res列，规则如下：

• 当Nat和Dat均为B时，取值为"Both are B"
• 当Nat和Dat均为A时，取值为"Both are A"
• 仅Dat为A时，取值为"Only Dat is A"
• 仅Nat为A时，取值为"Only Nat is A"

实现方法 #

方法1：Base R 嵌套ifelse

直接通过嵌套条件判断生成目标列，无需额外包：

df$res <- ifelse(df$Nat == "B" & df$Dat == "B", "Both are B",
                 ifelse(df$Nat == "A" & df$Dat == "A", "Both are A",
                        ifelse(df$Dat == "A", "Only Dat is A", "Only Nat is A")))

方法2：dplyr包case_when（可读性更强）

适合多规则场景，逻辑清晰易维护：

library(dplyr)

df <- df %>%
  mutate(res = case_when(
    Nat == "B" & Dat == "B" ~ "Both are B",
    Nat == "A" & Dat == "A" ~ "Both are A",
    Dat == "A" ~ "Only Dat is A",
    TRUE ~ "Only Nat is A"
  ))

方法3：映射表合并（适合规则扩展）

先定义规则映射表，再通过合并匹配结果：

# 创建规则映射表
map_table <- data.frame(
  Nat = c("B", "A", "B", "A"),
  Dat = c("B", "A", "A", "B"),
  res = c("Both are B", "Both are A", "Only Dat is A", "Only Nat is A")
)

# 合并得到结果
df <- merge(df, map_table, by = c("Nat", "Dat"), all.x = TRUE)

最终输出 #

运行任意一种方法后，得到的df即为期望结果：

> df
  Nat Dat            res
1   A   A     Both are A
2   A   B Only Nat is A
3   B   A Only Dat is A
4   B   B     Both are B
5   B   B     Both are B

内容的提问来源于stack exchange，提问作者Tpellirn