R 根据条件更改字符串

我有一个像下面这样的数据帧

我想在year变量中字符串的开头添加一个字符，它将基于第一个字符进行变量化

year <- c("991", "990", "985", "975", "001", "003")
name <- c("John", "Anna", "Amy", "Sarah", "Bob", "John")

test <- data.frame(year, name)

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有了这个，我得到了第一行的第一个字符，但我不知道如何将其放入循环中，然后在其中添加一个条件

这里有一个嵌套的

ifelse

语句

ifelse(substring(test$year, 1, 1) == 9, paste0(1, test$year), 
       ifelse(substring(test$year, 1, 1) == 0, paste0(2, test$year), paste0(7, test$year)))
#[1] "1991" "1990" "1985" "1975" "2001" "2003"

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这是一个嵌套的

ifelse

语句

ifelse(substring(test$year, 1, 1) == 9, paste0(1, test$year), 
       ifelse(substring(test$year, 1, 1) == 0, paste0(2, test$year), paste0(7, test$year)))
#[1] "1991" "1990" "1985" "1975" "2001" "2003"

library(data.table)
library(stringr)
setDT(test)

test[str_detect(year, "^0"), new := paste0("2", year)]
test[str_detect(year, "^9"), new := paste0("1", year)]