targets (version 0.4.1)

tar_timestamp: Get the timestamp(s) of a target.

Description

Get the time that a target's data was last modified. If there are multiple artifacts, as with file or URL targets, then multiple time stamps may be returned.

Usage

tar_timestamp(
  name = NULL,
  format = "%a, %d %b %Y %H:%M:%S",
  tz = "UTC",
  parse = TRUE
)

Arguments

name

Symbol, name of the target. If NULL (default) then tar_timestamp() will attempt to return the timestamp of the target currently running. Must be called inside a target's command or a supporting function in order to work.

format

Character of length 1, POSIXct format string passed to as.POSIXct() to parse the time stamp of a URL or AWS S3 bucket. Currently to targets with AWS-backed storage formats or format = "url". The default works with AWS S3 buckets but may not work for all URLs.

tz

Character of length 1, time zone of the original modification time recorded in the remote data (either a URL or S3 bucket; does not apply to locally stored targets). The tz argument is passed to as.POSIXct() to parse the time stamp of a URL or AWS S3 bucket. The time stamp of the return value is the time zone of the system, not the time zone originally recorded in the time stamp.

parse

Logical, whether to attempt to parse character string time stamps from URLs and data in AWS S3 buckets. Set to FALSE to debug. Debugging is important because incorrectly parsed time stamps will result in a return value of a POSIXct object at 1970-01-01 UTC instead of NA.

Value

If the target is not recorded in the metadata or cannot be parsed correctly, then tar_timestamp() returns a POSIXct object at 1970-01-01 UTC. If the target is recorded in the metadata and stored locally (i.e. the target is not a URL or AWS-backed format) then tar_timestamp() returns a vector of POSIXct modification times of the data files (in the order those files are listed in tar_meta(target_name, path)). The return values for URL and AWS targets depends on the parse argument. If parse is FALSE, then tar_timestamp() returns an unparsed character vector of the time stamps recorded on the web. If parse is TRUE, then tar_timestamp() attempts to convert those character time stamps into POSIXct objects displayed with the time zone of the current system. If the time stamp cannot be parsed with the given format, tar_timestamp() returns a POSIXct object at 1970-01-01 UTC (so parse = FALSE is helpful for debugging the format argument).

Details

tar_timestamp() checks the actual data, not the metadata, so the returned time stamps are more up-to-date than the ones from tar_meta().

See Also

Other utilities: tar_cancel(), tar_envir(), tar_group(), tar_name(), tar_path(), tar_seed(), tar_timestamp_raw()

Examples

# NOT RUN {
if (identical(Sys.getenv("TAR_LONG_EXAMPLES"), "true")) {
tar_dir({ # tar_dir() runs code from a temporary directory.
tar_script({
  list(tar_target(x, 1))
}, ask = FALSE)
tar_make()
# Get the timestamp.
tar_timestamp(x)
# We can use the timestamp to cancel the target
# if it already ran within the last hour.
# Be sure to set `cue = tar_cue(mode = "always")`
# if you want the target to always check the timestamp.
tar_script({
  list(
  tar_target(
    x,
    tar_cancel((Sys.time() - tar_timestamp()) < 3600),
    cue = tar_cue(mode = "always")
  )
)}, ask = FALSE)
tar_make()
})
}
# }