在 R data.table 中转换多列类的问题

Question

我想转换R中的变量列表data.table，但是，这种转换导致了意想不到的后果。我运行在 R 版本 4.0.1 下，库 data.table_1.12.8。这是一个简化的例子：

> dput(norw5)
structure(list(Born_before_2016 = c(1L, 1L, 1L, 1L, 1L), gender = c("2.Female", 
"1.Male", "2.Female", "1.Male", "1.Male"), payor = c("1:Private", 
"1:Private", "4:Other", "4:Other", "1:Private"), Age_in_day = c(0L, 
0L, 0L, 4L, 5L)), row.names = c(NA, -5L), class = c("data.table", 
"data.frame"), .internal.selfref = <pointer: 0x0000024ce5a41ef0>)

library(data.table)

fact <- c('Born_before_2016', 'gender', 'payor')

varls <- scan(text=fact, what = "", quiet = T)

factcols <- sapply(norw5[,..varls], is.numeric)

norw5new <- norw5[, names(norw5)[factcols] := lapply(.SD, as.character),
                  .SDcols = factcols]

> dput(norw5new)
structure(list(Born_before_2016 = c("1", "1", "1", "1", "1"), 
    gender = c("2.Female", "1.Male", "2.Female", "1.Male", "1.Male"
    ), payor = c("1:Private", "1:Private", "4:Other", "4:Other", 
    "1:Private"), Age_in_day = c("0", "0", "0", "4", "5")), row.names = c(NA, 
-5L), class = c("data.table", "data.frame"), .internal.selfref = <pointer: 0x0000024ce5a41ef0>)

如上所示，目标是找到数字变量（本例中为 Born_before_2016）并将它们转换为字符。但是，转换扩展到附加变量 Age_in_day，它根本不在列表中。我想不通，这里的 R 专家能否为我指明解决此问题的正确方向？谢谢！

Answer 1

factcols in .SDcols=factcols 应该是一个长度为4的逻辑向量或者第name/position列的向量，例如.SDcols = c("Born_before_2016"),.SDcols = 1，但 factcols <- sapply(norw5[,..varls], is.numeric) returns 长度为 3 的逻辑向量。可以固定为

fact <- c('Born_before_2016','gender','payor')
factcols <- sapply(norw5[,..fact], is.numeric)
cols <- names(norw5)[1:3][factcols]
norw5new <- norw5[,(cols) := lapply(.SD,as.character),.SDcols=cols]
norw5new 

#   Born_before_2016   gender     payor Age_in_day
#             <char>   <char>    <char>      <int>
#1:                1 2.Female 1:Private          0
#2:                1   1.Male 1:Private          0
#3:                1 2.Female   4:Other          0
#4:                1   1.Male   4:Other          4
#5:                1   1.Male 1:Private          5

在 R data.table 中转换多列 类 的问题

Issue converting multiple column classes in R data.table

r

data.table

在 R data.table 中转换多列类的问题