CODEWITHSUNDEEP
rr-s3
iod
iod

Reputation: 7592

When creating new class with its own method in R, why doesn't it autoprint when entering just the object name?

I'm trying to build my first ever R package. I started with a simple project that takes a date and "humanizes" it into the format "X [time unit] ago" (e.g., "3 days ago", "4 years ago" etc).

I wanted the result to have its own print method, so the value has a new class, and I defined a print.classname function.

When I run my new function and enter print(object) is works as expected. But when I just enter object, nothing shows. What might be causing this? Here's a shortened version of the function and the method:

humanize.now <- function(t) {
  now<-Sys.time()
  timediff<-diff(c(as.POSIXct(t), now))
  answer<-as.numeric(timediff)
  attributes(answer)<- list(unit=attributes(timediff)$units)
  answer<-trunc(answer)
  class(answer)<- "humanize"
  return(answer)
}

print.humanize <- function(h) {
  text<-paste0(h," ",attributes(h)$unit," ago")
  text
}

(Update: edited the humanize.now function since my abbreviation of it introduced a mistake. Now the resulting object should be of class "humanize")

Upvotes: 2

Views: 234

Answers (1)

Karolis Koncevičius
Karolis Koncevičius

Reputation: 9656

This is because your print.humanize() function doesn't print the value. If you add a line that prints text and returns it invisibly it should work:

print.humanize <- function(h) {
  text <- paste0(h, " ", attributes(h)$unit, " ago")
  print(text)
  invisible(text)
}

Upvotes: 4

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