转换模式数据帧 R

Question

关于如何将data.frame的所有值从一种模式转换为另一种模式的问题已经足够多了。这就提出了以下问题：如何在 R 中转换 data.frame 的特定列？我有以下几点：

# @param dataFrame the data.frame to be transformed
# @param start the column which first needs to be rewritten to numeric data
# @param end the column which needs to be rewritten to numeric data as last
# @param exlude the columns that need to be excluded from rewriting to numeric data

asNumericData <- function (dataFrame,start,end,exclude) {
   i <- start
   asNumericMatrix <- matrix(nrow = length(dataFrame), ncol = ncol(dataFrame))
   while (i <= end) {
       if (!(i %in% exclude)) {
          asNumericMatrix <- as.numeric(as.character(dataFrame[,i]))
       }
       i <- i + 1
   }
   return (asNumericMatrix)
}

但是，这会导致以下错误：

Error in asNumericMatrix[, i] <- as.numeric(as.character(dataFrame[, i])) : number of items to replace is not a multiple of replacement length

我做错了什么？关于如何将特定列（或更确切地说是排除列）从某种模式转换为另一种模式的任何其他建议也欢迎。

Answer 1

这是我过去的做法。给定一个列向量，迭代它们（通过 lapply），然后做你的 as.character、as.numeric、as.factor 等......

df <- data.frame(v=c("B","C","A"), w=c(12,14,17), h=c(1,2,3))
> str(df)
'data.frame':   3 obs. of  3 variables:
 $ v: Factor w/ 3 levels "A","B","C": 2 3 1
 $ w: num  12 14 17
 $ h: num  1 2 3
cols <- c("w", "h")
df[,cols] <- lapply(df[,cols], as.character)
> str(df)
'data.frame':   3 obs. of  3 variables:
 $ v: Factor w/ 3 levels "A","B","C": 2 3 1
 $ w: chr  "12" "14" "17"
 $ h: chr  "1" "2" "3"