如果可能，将列转换为数字在函数中不起作用

Question

我有如下示例数据：

library(data.table)
set.seed(1)
DT <- data.table(panelID = sample(50,50),                                                    # Creates a panel ID
                      Country = c(rep("Albania",30),rep("Belarus",50), rep("Chilipepper",20)),       
                      some_NA = sample(0:5, 6),                                             
                      some_NA_factor = sample(0:5, 6),         
                      Group = c(rep(1,20),rep(2,20),rep(3,20),rep(4,20),rep(5,20)),
                      Time = rep(seq(as.Date("2010-01-03"), length=20, by="1 month") - 1,5),
                      wt = 15*round(runif(100)/10,2),
                      Income = round(rnorm(10,-5,5),2),
                      Happiness = sample(10,10),
                      Sex = round(rnorm(10,0.75,0.3),2),
                      Age = sample(100,100),
                      Educ = round(rnorm(10,0.75,0.3),2))           
DT [, uniqueID := .I]                                                                        # Creates a unique ID                                                                                # 
DT$some_NA_factor <- factor(DT$some_NA_factor)
DT$Group <- as.character(DT$Group)
DT2 <- copy(DT)

这就是我想要做的，如果可能的话，将列（在本例中为第 5 列 Group）转换为数字。

dfs <- c("DT", "DT2")
conv_to_num_check <- function(z) is.character(z) && (mean(grepl("^ *-?[\d.]+(?:e-?\d+)?$", z, perl = TRUE), na.rm=TRUE)>0.9)

for (i in length(dfs)) {
  cols <- which(sapply(get(dfs[i]), conv_to_num_check))
  setDT(get(dfs[i]))[, (cols) := lapply(.SD, as.numeric), .SDcols = cols]
}

但是当我检查 class 时：

class(DT$Group) # Is character

当我这样做时：

cols <- which(sapply(DT, conv_to_num_check))
setDT(DT)[, (cols) := lapply(.SD, as.numeric), .SDcols = cols]
class(DT$Group) # Is numeric

有效..我做错了什么？

Answer 1

只是 for (i in length(dfs)) 行中的一个小错误，因为 length(dfs) 只是 returns 2:

for (i in length(dfs)) {
    print(i)
}
# [1] 2

如果您将其更改为：

，它将起作用

for (i in seq_along(dfs)) {
  cols <- which(sapply(get(dfs[i]), conv_to_num_check))
  setDT(get(dfs[i]))[, (cols) := lapply(.SD, as.numeric), .SDcols = cols]
}

如果可能，将列转换为数字在函数中不起作用

Converting columns to numeric if possible does not work within a function

r

numeric

character

data.table