使用for循环和“粘贴”创建多个变量

Question

library(tidyverse)
library(magrittr)

df <- data.frame(year = c(1977:1981), set852 = c(1,1,0,0,0), set857=c(0,0,1,1,0), set874=c(0,0,0,1,1))

对于每个变量 set852、set857 等（在真实数据集中，这是一个很长的列表），我想创建一个变量来指示时间序列是否有变化（值将是“开始”、“结束”和“不用找了”）。附加变量应如下所示：

df_final <- data.frame(year = c(1977:1981), c852 = c("start","end","no change","no change","no change"), c857=c("no change","no change","start","end","no change"), c874=c("no change","no change","no change","start","end"))

我在 tidyverse 中尝试使用 for-loop、mutate、paste 和 case_when：

set_num <- as.integer(str_extract(colnames(df), "[0-9]+"))

for (i in 2:nrow(df))
{
  df %<>% mutate(paste0("c", set_num[[i]]) = case_when(paste("set", set_num[[i]], sep="")==1 & year == 1977 ~ "start",
             paste("set", set_num[[i]], sep="")==1 & lag(paste("set", set_num[[i]], sep=""))==0 ~ "start",
             paste("set", set_num[[i]], sep="")==1 & lead(paste("set", set_num[[i]], sep=""))==0 ~ "end",
TRUE~"no change"))
}

但是，mutate之后的paste-function不会被识别为函数，而是被识别为以“paste0(”c”....等等”开头的变量的名称。如何获取注册paste0的代码-函数作为函数而不是字符串？

Answer 1

代替 for 循环，您可以使用

dplyr::across

来实现所需的结果，如下所示：

library(dplyr, warn = FALSE)

df <- data.frame(
  year = c(1977:1981),
  set852 = c(1, 1, 0, 0, 0),
  set857 = c(0, 0, 1, 1, 0),
  set874 = c(0, 0, 0, 1, 1)
)

myfun <- function(.x, year) {
  case_when(
    .x == 1 & year == 1977 ~ "start",
    .x == 1 & lag(.x) == 0 ~ "start",
    .x == 1 & lead(.x) == 0 ~ "end",
    .default = "no change"
  )
}

set_cols <- grep("\\d+$", names(df), value = TRUE)

df |>
  mutate(
    across(all_of(set_cols), ~ myfun(.x, year),
      .names = "{gsub('^.*?(\\\\d+)$', 'c\\\\1', .col)}"
    )
  ) |> 
  select(-all_of(set_cols))
#>   year      c852      c857      c874
#> 1 1977     start no change no change
#> 2 1978       end no change no change
#> 3 1979 no change     start no change
#> 4 1980 no change       end     start
#> 5 1981 no change no change no change