r - 在 for 循环中分配不同的类

Question

我想编写一个 for 循环，其中我需要先将 data.frame 的某些列的类转换为字符。经过一些操作(与此问题无关)后，我需要将列转换回其原始类。

列到它们原始类的转换必须在 for 循环中完成。我怎么能那样做？

这是一些数据和一个示例性的 for 循环:

# Example data
data <- data.frame(x1 = as.numeric(1:5), x2 = as.factor(7:3))

for(i in 1:ncol(data)) {

  # Save original class.
  class_col_i <- class(data[ , i])

  # Convert column as character.
  data[ , i] <- as.character(data[ , i])

  # (Here I will do some operations, which are irrelevant for this problem.)

  # Here I need to convert the column back to its original class.
  # How can I do that?

  # data[ , i] <- class_col_i... ???
}

class(data$x1) # This should be a numeric
class(data$x2) # This should be a factor

Answer 1

使用match.fun，看这个例子:

#dummy data
d <- mtcars
class(d$gear)
# [1] "numeric"

#change to character
classOrg <- class(d$gear)
d$gear <- as.character(d$gear)
class(d$gear)
# [1] "character"

#do some fun stuff
# ... d$gear 

#convert it back
myConvertFun <- match.fun(paste0("as.", classOrg))
d$gear <- myConvertFun(d$gear)
class(d$gear)
# [1] "numeric"