Creating a function to make a new column

Question

Hey all I apologise if this is very simple and mediocre but I can't seem to create a function that turns a time variable (00:00:00) into a numeric AND creates a new column to put the result in.

I can turn the time into a numeric, I just cannot complete the 'new column' part. Any help is appreciated.

Time <- function(x) {
   begin <- x$avg..wait.time
  x$Num.wait.time <- as.numeric(as.POSIXct(strptime(begin, "%H:%M:%S")))
}

(NOTE: avg..wait.time is the time cell and Num.wait.time is the new variable/column I want to create)

Welcome to StackOverflow! Please read the info about [how to ask a good question](http://stackoverflow.com/help/how-to-ask) and how to give a [reproducible example](http://stackoverflow.com/questions/5963269). This will make it much easier for others to help you. — Ronak Shah, Jul 27 '18 at 01:10
I wouldn't make a function that adds a column - make the function just do your conversion on a vector and then add the column outside of the function like `df$newvar <- Time(df$avg.wait.time)` where `Time` is `Time <- function(x) as.numeric(as.POSIXct(x, format="%H:%M:%S"))` — thelatemail, Jul 27 '18 at 03:12

Kim · Accepted Answer · 2018-07-27T01:40:37.097

1

If your purpose is not in writing the function per se, with dplyr you can directly tackle the problem with existing wheels, and not have to write a separate function.

library(dplyr)
df <- data.frame(avg.wait.time = c("01:02:03", "03:02:01"))
df <- df %>% 
  dplyr::mutate(
    avg.wait.numeric = as.numeric(as.POSIXct(strptime(avg.wait.time, "%H:%M:%S")))
  )

If you wish to write a separate function, I would do as follows:

Time <- function(x, 
                 input_var = "avg.wait.time", 
                 output_var = "avg.wait.numeric") {
  x[[output_var]] <- 
    as.numeric(as.POSIXct(strptime(x[[input_var]], "%H:%M:%S")))
  return(x)
}

This allows the input variable name and output variable name to be specified, currently set with some arbitrary default values (you can kick these out, of course).

edited Jul 27 '18 at 01:40

answered Jul 27 '18 at 01:32

Kim

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This works a charm thank you, It returns the appropriate value. Although, I can't call on `avg.wait.numeric` after I run the function. Is there a simple way I can run the function, and still have the column to call on afterwards? – Jack Jul 27 '18 at 01:48
@Jack Uhh, could you clarify a little bit? Perhaps you mean that simply running `Time(df)` will show a wrangled dataframe but not stored in the global environment. You would need to do `df <- Time(df)` if you wish to overwrite the existing dataframe? – Kim Jul 27 '18 at 01:53
Sorry for my lack of communication, this is my first time asking a question on Stack Overflow. That is what I meant to say, thank you. Problem solved! – Jack Jul 27 '18 at 01:57
@Jack Magnificent! Feel free to accept the answer if you found it useful. – Kim Jul 27 '18 at 01:58

Creating a function to make a new column

1 Answers1