Trying to make mutate_at work with strptime

Question

I have the following data frame: df = data.frame(date = "23-12-09 22:52") This code works fine: strptime(df$date, "%d-%m-%y %H:%M") # [1] "2009-12-23 22:52:00 CET"` But if I try it using mutate_at I get an error: dplyr::mutate_at(df, vars(date), strptime, "%d-%m-%y %H:%M") Error in mutate_impl(.data, dots) : Column "date" is of unsupported class POSIXlt` I would like to understand why my mutate_at statement doesn't work. (I don't need an alternative solution. This question is purely educational.) JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

Answer 1

After applying strptime class of date column becomes POSIXlt class(strptime(df$date, "%d-%m-%y %H:%M")) #[1] "POSIXlt" "POSIXt" dplyr doesn't want to handle objects of class POSIXlt because of the reasons mentioned here. So you need to have objects of other class in dplyr chain. Maybe a character dplyr::mutate_at(df, vars(date), ~ as.character(strptime(., "%d-%m-%y %H:%M"))) # date #1 2009-12-23 22:52:00 Or a POSIXct object dplyr::mutate_at(df, vars(date), ~ as.POSIXct(., format = "%d-%m-%y %H:%M")) # date #1 2009-12-23 22:52:00