Base R operations on a tbl_now

A tbl_now() is a tibble with extra attributes recording which column is the event date, which is the report date, and so on. These methods make sure those attributes survive ordinary base-R manipulation, so that x[1:10, ], names(x) <- ... and x$new <- ... give you back a tbl_now rather than a bare data frame.

You never call them directly – they are what makes the operators work.

Usage

# S3 method for class 'tbl_now'
x[...]

# S3 method for class 'grouped_tbl_now'
x[...]

# S3 method for class 'tbl_now'
names(x) <- value

# S3 method for class 'grouped_tbl_now'
names(x) <- value

# S3 method for class 'tbl_now'
x$name <- value

# S3 method for class 'grouped_tbl_now'
x$name <- value

Arguments

x

A tbl_now object.

...

Passed to the underlying [ method: rows and columns to keep.

value

For names<- and $<-, the replacement value.

name

For $<-, the column being assigned to.

Value

A tbl_now object, or a plain data frame when the operation invalidated the class.

Details

When an operation leaves the object unable to describe a nowcast – because it dropped or renamed the event-date column, say – the class cannot honestly be kept. In that case the result is demoted to a plain data frame (with a warning), rather than pretending to still be a tbl_now. Attributes that are still meaningful are preserved on the way down.

The same applies to dplyr verbs, through dplyr_reconstruct().

See also

tbl_now() for the attributes being preserved; tbl_now_attributes() to check what survived; as_tibble() to drop the class on purpose; validate_tbl_now() to confirm the result is still well formed.

Examples

data(denguedat)
dengue <- tbl_now(denguedat,
  event_date = onset_week, report_date = report_week,
  strata = gender, verbose = FALSE
)

# Subsetting rows keeps the class and everything it knows.
small <- dengue[1:10, ]
class(small)[1]
#> [1] "tbl_now"
get_event_date(small)
#> [1] "onset_week"

# So does adding a column with `$<-`.
dengue$season <- ifelse(
  lubridate::month(dengue$onset_week) %in% 6:11, "wet", "dry"
)
class(dengue)[1]
#> [1] "tbl_now"

# And renaming an unimportant column with `names<-`.
renamed <- dengue
names(renamed)[names(renamed) == "season"] <- "period"
get_event_date(renamed)
#> [1] "onset_week"

# But dropping the event date leaves nothing a nowcast could use, so the
# object is demoted to a plain tibble instead of lying about itself.
demoted <- suppressWarnings(dengue[, c("report_week", "gender")])
class(demoted)[1]
#> [1] "tbl_df"