用於轉換數據幀列類型的函數

Question

R通常以「錯誤」格式理解數據幀列，或者您只需要將因子列中的列類更改爲字符以便對其進行修改。我一直在改變柱類以下方式以前：

set.seed(1) 

df <- data.frame(x = 1:10, 
y = rep(1:2, 5), 
k = rnorm(10, 5,2), 
z = rep(c(2010, 2012, 2011, 2010, 1999), 2), 
j = c(rep(c("a", "b", "c"), 3), "d")) 

x <- c("y", "z") 

for(i in 1:length(x)){ 
df[,x[i]] <- factor(df[,x[i]])} 

再換數字：

x <- 1:5 

for(i in 1:length(x)){ 
df[,x[i]] <- as.numeric(as.character(df[,x[i]]))} # Character cannot become numeric 

它發生，我認爲也許有一個更好的方式這樣做。我發現this question，這幾乎正是我需要的：

convert.magic <- function(obj,types){ 
out <- lapply(1:length(obj),FUN = function(i){FUN1 <- 
switch(types[i], 
character = as.character, 
numeric = as.numeric, 
factor = as.factor); FUN1(obj[,i])}) 
names(out) <- colnames(obj) 
as.data.frame(out) 
} 

然而，對於這個功能載體類型都有每一列中指定：

convert.magic(df, rep("factor",5)) 

convert.magic(df, c("character", "factor")) 
# Error in FUN(1:5[[1L]], ...) : could not find function "FUN1" 

有人能幫助我重建這個功能，所以它可以與列名和數字一起工作嗎？恐怕這將是對我來說太先進...

x <- c("y", "z") 
convert.magic(df, "character", x) 

Answer 1

df <- data.frame(x = 1:10, 
       y = rep(1:2, 5), 
       k = rnorm(10, 5,2), 
       z = rep(c(2010, 2012, 2011, 2010, 1999), 2), 
       j = c(rep(c("a", "b", "c"), 3), "d")) 

convert.magic <- function(obj, type){ 
    FUN1 <- switch(type, 
       character = as.character, 
       numeric = as.numeric, 
       factor = as.factor) 
    out <- lapply(obj, FUN1) 
    as.data.frame(out) 
} 

str(df) 
str(convert.magic(df, "character")) 
str(convert.magic(df, "factor")) 
df[, c("x", "y")] <- convert.magic(df[, c("x", "y")], "factor")