r - 自动转换 data.frame 列

Question

我对一种自动将由因子列(如 df)组成的数据框转换为最佳可能类型的方法感兴趣，类似于 read.table 创建的内容(如 df2)。一种可能是将数据帧写入字符串并使用 read.table 将其读回。还有其他的吗？

> df <- data.frame(a=c(" 1"," 2", " 3"),b=c("a","b","c"),c=c(" 1.0", "NA", " 2.0"),d=c(" 1", "B", "2"))
> str(df)
'data.frame':   3 obs. of  4 variables:
 $ a: Factor w/ 3 levels " 1"," 2"," 3": 1 2 3
 $ b: Factor w/ 3 levels "a","b","c": 1 2 3
 $ c: Factor w/ 3 levels " 1.0"," 2.0",..: 1 3 2
 $ d: Factor w/ 3 levels " 1","2","B": 1 3 2
> df2 <- with(df, data.frame(a=as.integer(a),b=b,c=as.numeric(c),d=as.character(d), stringsAsFactors=FALSE))
> str(df2)
'data.frame':   3 obs. of  4 variables:
 $ a: int  1 2 3
 $ b: Factor w/ 3 levels "a","b","c": 1 2 3
 $ c: num  1 3 2
 $ d: chr  " 1" "B" "2"

Answer 1

使用read.table使用的函数:type.convert。

示例:

df <- data.frame(a=c(" 1"," 2", " 3"), b=c("a","b","c"), 
                 c=c(" 1.0", "NA", " 2.0"), d=c(" 1", "B", "2"))
str(df)
# 'data.frame':  3 obs. of  4 variables:
#  $ a: Factor w/ 3 levels " 1"," 2"," 3": 1 2 3
#  $ b: Factor w/ 3 levels "a","b","c": 1 2 3
#  $ c: Factor w/ 3 levels " 1.0"," 2.0",..: 1 3 2
#  $ d: Factor w/ 3 levels " 1","2","B": 1 3 2
df[] <- lapply(df, function(y) type.convert(as.character(y)))
df
#   a b  c  d
# 1 1 a  1  1
# 2 2 b NA  B
# 3 3 c  2  2
str(df)
# 'data.frame':  3 obs. of  4 variables:
#  $ a: int  1 2 3
#  $ b: Factor w/ 3 levels "a","b","c": 1 2 3
#  $ c: num  1 NA 2
#  $ d: Factor w/ 3 levels " 1","2","B": 1 3 2

(但我不确定这是否是您正在寻找的......)

---

更新:如果你想创建一个colClasses类型的函数，也许你可以尝试这样的函数。与您的问题标题不同，这不是“自动”，但它确实允许您指定每列的列类，而不是由 type.convert 来决定。

toColClasses <- function(inDF, colClasses) {
  if (length(colClasses) != length(inDF)) stop("Please specify colClasses for each column")
  inDF[] <- lapply(seq_along(colClasses), function(y) {
    if (colClasses[y] == "") inDF[y] <- inDF[[y]]
    else {
      FUN <- match.fun(colClasses[y])
      inDF[y] <- suppressWarnings(FUN(as.character(inDF[[y]])))
    }
  })
  inDF
}

您可以按如下方式使用它:

df <- data.frame(a = c(" 1"," 2", " 3"), b = c("a","b","c"), 
                 c = c(" 1.0", "NA", " 2.0"), d = c(" 1", "B", "2"))

df2 <- toColClasses(df, c("as.integer", "", "as.numeric", "as.character"))
df2
#   a b  c  d
# 1 1 a  1  1
# 2 2 b NA  B
# 3 3 c  2  2
str(df2)
# 'data.frame':  3 obs. of  4 variables:
#  $ a: int  1 2 3
#  $ b: Factor w/ 3 levels "a","b","c": 1 2 3
#  $ c: num  1 NA 2
#  $ d: chr  " 1" "B" "2"

不过，您必须对该函数做更多的工作才能使其接受更广泛的 as... 函数。