R：如何按列删除重复行[重复]

df <- data.frame(id = c(1, 1, 1, 2, 2),
                 gender = c("Female", "Female", "Male", "Female", "Male"),
                 variant = c("a", "b", "c", "d", "e"))
> df
  id gender variant
1  1 Female       a
2  1 Female       b
3  1   Male       c
4  2 Female       d
5  2   Male       e

我想根据以下内容删除 data.frame 中的重复行gender我的数据集中的列。我知道有人问过类似的问题（here）但这里的区别是我想删除数据集的每个子集中的重复行，其中每个子集由唯一的定义id.

我想要的结果是这样的：

  id gender variant
1  1 Female       a
3  1   Male       c
4  2 Female       d
5  2   Male       e

我已经尝试过以下方法并且它有效，但我想知道是否有更干净、更有效的方法来做到这一点？

out = list()
for(i in 1:2){
  df2 <- subset(df, id == i)
  out[[i]] <- df2[!duplicated(df2$gender), ]
}
do.call(rbind.data.frame, out)

df[!duplicated(df[ , c("id","gender")]),]

#     id  gender  variant
#  1   1  Female     a
#  3   1   Male      c
#  4   2  Female     d
#  5   2   Male      e

另一种方法是使用subset如下：

subset(df, !duplicated(subset(df, select=c(id, gender))))

#   id  gender variant
# 1  1  Female     a
# 3  1    Male     c
# 4  2  Female     d
# 5  2    Male     e