在for循環中分配不同的類

Question

我想編寫一個for循環，其中我需要首先將data.frame的某些列的類轉換爲字符。經過一些操作（這與這個問題無關），我需要將列轉換回原來的類。

將列轉換爲其原始類必須在for循環中完成。我怎麼能這樣做？

下面是一些數據和循環示範：

# 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，看下面的例子：

#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" 

Answer 2

試試這個：

data <- data.frame(x1 = as.numeric(1:5), x2 = as.factor(7:3)) 
class_col<-NULL 
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? 

class(data[ , i]) <- class_col[i] 
} 

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