在现有列上创建一个新列，但在上面排

Question

我想基于现有列创建一个新列，但是

上面有一行

从：

开始

df <- data.frame(a=c(1:10), b=c("red", "yellow", "blue", "green", "yellow", "purple", "blue", "green", "yellow", "purple"))

结果如下：

df <- data.frame(a=c(1:10), b=c("red", "yellow", "blue", "green", "yellow", "purple", "blue", "green", "yellow", "purple"), c=c("na", "red", "yellow", "blue", "green", "yellow", "purple", "blue", "green", "yellow"))

感谢您提供的任何帮助

Answer 1

来自包shift的{​​{1}}的一种方式：

data.table

Answer 2

使用dplyr可以使用mutate和lag函数完成此操作：

library(dplyr)
mutate(df, c = lag(b))

#>     a      b      c
#> 1   1    red   <NA>
#> 2   2 yellow    red
#> 3   3   blue yellow
#> 4   4  green   blue
#> 5   5 yellow  green
#> 6   6 purple yellow
#> 7   7   blue purple
#> 8   8  green   blue
#> 9   9 yellow  green
#> 10 10 purple yellow