merge()：如何在结果中保留 by.x 和 by.y 定义的两列

Question

给出 ?merge 手册页中的示例数据：

authors <- data.frame(
    ## I(*) : use character columns of names to get sensible sort order
    surname = I(c("Tukey", "Venables", "Tierney", "Ripley", "McNeil")),
    nationality = c("US", "Australia", "US", "UK", "Australia"),
    deceased = c("yes", rep("no", 4)))
authorN <- within(authors, { name <- surname; rm(surname) })
books <- data.frame(
    name = I(c("Tukey", "Venables", "Tierney",
             "Ripley", "Ripley", "McNeil", "R Core")),
    title = c("Exploratory Data Analysis",
              "Modern Applied Statistics ...",
              "LISP-STAT",
              "Spatial Statistics", "Stochastic Simulation",
              "Interactive Data Analysis",
              "An Introduction to R"),
    other.author = c(NA, "Ripley", NA, NA, NA, NA,
                     "Venables & Smith"))

我愿意：

m <- merge(authors, books, by.x = "surname", by.y = "name", all = TRUE)

并得到：

> head(authors,3)
   surname nationality deceased
1    Tukey          US      yes
2 Venables   Australia       no
3  Tierney          US       no
> head(books,3)
      name                         title other.author
1    Tukey     Exploratory Data Analysis         <NA>
2 Venables Modern Applied Statistics ...       Ripley
3  Tierney                     LISP-STAT         <NA>
> 
> head(m,3)
  surname nationality deceased                     title     other.author
1  McNeil   Australia       no Interactive Data Analysis             <NA>
2  R Core        <NA>     <NA>      An Introduction to R Venables & Smith
3  Ripley          UK       no        Spatial Statistics             <NA>

输出 m 中缺少书籍中的“名称”列。我有什么办法可以保留它吗？除此之外，我需要注意数据集中“by”变量之间的无意差异（例如拼写错误）。

Answer 1

在合并的数据帧 m 中，不会保留作者数据帧中的列姓氏，因为您正在按此列进行合并，并且它会被书籍数据帧中的列名称替换。

但是您可以向 m 数据框添加名称列并分配一个值，就像我在下面的代码中所做的那样

m$name <- NA # Create a new column 'name' and initialize it with NA values
m$name[!is.na(m$surname)] <- m$surname[!is.na(m$surname)] # Copy values from 'surname' to 'name' where 'surname' is not NA
m