Filter out all data frames which don't have the column Z in a list of data frames?

I have a list of six data frames, from which 5/6 data frames have a column "Z". To proceed with my script, I need to remove the data frame which doesn’t have column Z, so I tried the following code:

for(i in 1:length(df)){
  if(!("Z" %in% colnames(df[[i]])))
  {
    df[[i]] = NULL
  }
}

This seem’d to actually do the job (it removed the one data frame from the list, which didn’t have the column Z), BUT however I still got a message "Error in df[[i]] : subscript out of bounds". Why is that, and how could I get around the error?

>Solution :

If df is your list of 6 dataframes, you can do this:

df <- df[sapply(df, \(i) "Z" %in% colnames(i))]

The reason you get the error is that your loop will reduce the length of df, such that i will eventually be beyond the (new) length of df. There will be no error if the only frame in df without column Z is the last frame.