R-循环几个文件

Question

I want to apply this code on several lists of dataframes (df).

df1<- lapply(df1, function(x) {
  x$Date <- as.Date((x$Date), format="%Y-%m-%d")
  x})

The dataframe lists are called df1 , df2 , df3 , df4 and abc1 , abc2 , abc3 , abc4 . The Date-column is always on the same place.

I tried this to get the df1-4 done, but it doesn't work.

for (i in 1:4) {
  df[i] <- lapply(df[i], function(x) {
  x$Date <- as.Date((x$Date), format="%Y-%m-%d")
  x})}

I also thought about getting all the filenames into a list and looping with that:

df_list = c("df1","df2", "df3", "df4", "abc1", "abc2", "abc3", "abc4")

But I haven't succeeded with that. I want to keep the original names of the files. Any suggestions?

Answer 1

for(i in 1:length(df_list)) {
  df_list[[i]] <- lapply(df_list[[i]], function(x) {
    x$Date <- as.Date((x$Date), format="%Y-%m-%d")
    x})
}

Does this work for you?

For me it does:

class(df_list[[1]][[1]]$Date)
[1] "Date"

Your error seemed to happen because you used [] instead of [[]] . You have to use double brackets to refer to the data.frame.