重新排序大型数据框中的列

Question

使用以下示例数据帧:

a <-  c(1:5)
b <- c("Cat", "Dog", "Rabbit", "Cat", "Dog")
c <- c("Dog", "Rabbit", "Cat", "Dog", "Dog")
d <- c("Rabbit", "Cat", "Dog", "Dog", "Rabbit")
e <- c("Cat", "Dog", "Dog", "Rabbit", "Cat")
f <- c("Cat", "Dog", "Dog", "Rabbit", "Cat")

df <- data.frame(a,b,c,d,e,f)

我想调查如何重新排序列而不必输入所有列名,即, df[,c("a","d","e","f","b","c")]

我怎么说我想要列f和列f后的列？(仅引用我要移动的列或列范围？).

非常感谢您的帮助.

Answer 1

移动特定的列的开头或data.frame的结束,使用select从dplyr包及其everything()功能.在这个例子中,我们发送到最后:

library(dplyr)
df %>%
  select(-b, -c, everything())

  a      d      e      f      b      c
1 1 Rabbit    Cat    Cat    Cat    Dog
2 2    Cat    Dog    Dog    Dog Rabbit
3 3    Dog    Dog    Dog Rabbit    Cat
4 4    Dog Rabbit Rabbit    Cat    Dog
5 5 Rabbit    Cat    Cat    Dog    Dog

没有否定,列将被发送到前面.

Answer 2

如果您只是将某些列移动到最后,您可以创建一个小帮助函数,如下所示:

movetolast <- function(data, move) {
  data[c(setdiff(names(data), move), move)]
}

movetolast(df, c("b", "c"))
#   a      d      e      f      b      c
# 1 1 Rabbit    Cat    Cat    Cat    Dog
# 2 2    Cat    Dog    Dog    Dog Rabbit
# 3 3    Dog    Dog    Dog Rabbit    Cat
# 4 4    Dog Rabbit Rabbit    Cat    Dog
# 5 5 Rabbit    Cat    Cat    Dog    Dog

我不建议过于习惯使用列位置,特别是从程序角度来看,因为这些位置可能会改变.

"为了好玩"更新

这是对上述功能的扩展解释.它允许您将列移动到第一个或最后一个位置,或者移动到另一个列之前或之后.

moveMe <- function(data, tomove, where = "last", ba = NULL) {
  temp <- setdiff(names(data), tomove)
  x <- switch(
    where,
    first = data[c(tomove, temp)],
    last = data[c(temp, tomove)],
    before = {
      if (is.null(ba)) stop("must specify ba column")
      if (length(ba) > 1) stop("ba must be a single character string")
      data[append(temp, values = tomove, after = (match(ba, temp)-1))]
    },
    after = {
      if (is.null(ba)) stop("must specify ba column")
      if (length(ba) > 1) stop("ba must be a single character string")
      data[append(temp, values = tomove, after = (match(ba, temp)))]
    })
  x
}

尝试使用以下内容.

moveMe(df, c("b", "c"))
moveMe(df, c("b", "c"), "first")
moveMe(df, c("b", "c"), "before", "e")
moveMe(df, c("b", "c"), "after", "e")

您需要调整它以进行一些错误检查 - 例如,如果您尝试将列"b"和"c"移动到"c之前",您(显然)会收到错误.

Answer 3

您可以按位置引用列.例如

df <- df[ ,c(1,4:6,2:3)]
> df
  a      d      e      f      b      c
1 1 Rabbit    Cat    Cat    Cat    Dog
2 2    Cat    Dog    Dog    Dog Rabbit
3 3    Dog    Dog    Dog Rabbit    Cat
4 4    Dog Rabbit Rabbit    Cat    Dog
5 5 Rabbit    Cat    Cat    Dog    Dog

Answer 4

包dplyr和函数dplyr::relocate是 中引入的一个新动词dplyr 1.0.0，它以高度可读的语法完全满足您的要求。

df %>% dplyr::relocate(b, c, .after = f)