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Parse POSIXct or Date objects from input data

Source: R/anytime.R
anytime.Rd

These function use the Boost Date_Time library to parse datetimes (and dates) from strings, integers, factors or even numeric values (which are cast to strings internally). They return a vector of POSIXct objects (or Date objects in the case of anydate). POSIXct objects represent dates and time as (possibly fractional) seconds since the ‘epoch’ of January 1, 1970. A timezone can be set, if none is supplied ‘UTC’ is set.

Usage

anytime(x, tz = getTZ(), asUTC = FALSE,
  useR = getOption("anytimeUseRConversions", FALSE),
  oldHeuristic = getOption("anytimeOldHeuristic", FALSE),
  calcUnique = FALSE)

anydate(x, tz = getTZ(), asUTC = FALSE,
  useR = getOption("anytimeUseRConversions", FALSE), calcUnique = FALSE)

utctime(x, tz = getTZ(), useR = getOption("anytimeUseRConversions", FALSE),
  oldHeuristic = getOption("anytimeOldHeuristic", FALSE),
  calcUnique = FALSE)

utcdate(x, tz = getTZ(), useR = getOption("anytimeUseRConversions", FALSE),
  calcUnique = FALSE)

Arguments

x

A vector of type character, integer or numeric with date(time) expressions to be parsed and converted.

tz

A string with the timezone, defaults to the result of the (internal) getTZ function if unset. The getTZ function returns the timezone values stored in local package environment, and set at package load time. Also note that this argument applies to the output: the returned object will have this timezone set. The timezone is not used for the parsing which will always be to localtime, or to UTC is the asUTC variable is set (as it is in the related functions utctime and utcdate). So one can think of the argument as ‘shift parsed time object to this timezone’. This is similar to what format() in base R does, but our return value is still a POSIXt object instead of a character value.

asUTC

A logical value indicating if parsing should be to UTC; default is false implying localtime.

useR

A logical value indicating if conversion should be done via code from R (via Rcpp::Function) instead of the default Boost routines. The default value is the value of the option anytimeUseRConversions with a fallback of FALSE if the option is unset. In other words, this will be false by default but can be set to true via an option.

oldHeuristic

A logical value to enable behaviour as in version 0.2.2 or earlier: interpret a numeric or integer value that could be seen as a YYYYMMDD as a date. If the default value FALSE is seen, then numeric values are used as offsets dates (in anydate or utcdate), and as second offsets for datetimes otherwise. A default value can also be set via the anytimeOldHeuristic option.

calcUnique

A logical value with a default value of FALSE that tells the function to perform the anytime() or anydate() calculation only once for each unique value in the x vector. It results in no difference in inputs or outputs, but can result in a significant speed increases for long vectors where each timestamp appears more than once. However, it will result in a slight slow down for input vectors where each timestamp appears only once.

Value

A vector of POSIXct elements, or, in the case of anydate, a vector of Date objects.

Details

A number of fixed formats are tried in succession. These include the standard ISO format ‘YYYY-MM-DD HH:MM:SS’ as well as different local variants including several forms popular in the United States. Two-digits years and clearly ambigous formats such as ‘03/04/05’ are ignored. In the case of parsing failure a NA value is returned.

Fractional seconds are supported as well. As R itself only supports microseconds, the Boost compile-time option for nano-second resolution has not been enabled.

Notes

By default, the (internal) conversion to (fractional) seconds since the epoch is relative to the locatime of this system, and therefore not completely independent of the settings of the local system. This is to strike a balance between ease of use and functionality. A more-full featured conversion could be possibly be added with support for arbitrary reference times, but this is (at least) currently outside the scope of this package. See the RcppCCTZ package which offers some timezone-shifting and differencing functionality. As of version 0.0.5 one can also parse relative to UTC avoiding the localtime issue,

Times and timezones can be tricky. This package offers a heuristic approach, it is likely that some input formats may not be parsed, or worse, be parsed incorrectly. This is not quite a Bobby Tables situation but care must always be taken with user-supplied input.

The Boost Date_Time library cannot parse single digit months or days. So while ‘2016/09/02’ works (as expected), ‘2016/9/2’ will not. Other non-standard formats may also fail.

There is a known issue (discussed at length in issue ticket 5) where Australian times are off by an hour. This seems to affect only Windows, not Linux.

When given a vector, R will coerce it to the type of the first element. Should that be NA, surprising things can happen: c(NA, Sys.Date()) forces both values to numeric and the date will not be parsed correctly (as its integer value becomes numeric before our code sees it). On the other hand, c(Sys.Date(), NA) works as expected parsing as type Date with one missing value. See issue ticket 11 for more.

Another known issue concerns conversion when the timezone is set to ‘Europe/London’, see GitHub issue tickets 36. 51. 59. and 86. As pointed out in the comment in that last one, the Sys.timezone manual page suggests several alternatives to using ‘Europe/London’ such as ‘GB’.

Yet another known issue arises on Windows due to designs in the Boost library. While we can set the TZ library variable, Boost actually does not consult it but rather relies only on the (Windows) tool tzutil. This means that default behaviour should be as expected: dates and/or times are parsed to the local settings. But testing different TZ values (or more precisely, changes via the (unexported) helper function setTZ function as we cache TZ) will only influence the behaviour on Unix or Unix-alike operating systems and not on Windows. See the discussion at issue ticket 96 for more. In short, the recommendation for Windows user is to also set useR=TRUE when setting a timezone argument.

Operating System Impact

On Windows systems, accessing the isdst flag on dates or times before January 1, 1970, can lead to a crash. Therefore, the lookup of this value has been disabled for those dates and times, which could therefore be off by an hour (the common value that needs to be corrected). It should not affect dates, but may affect datetime objects.

Old Heuristic

Up until version 0.2.2, numeric input smaller than an internal cutoff value was interpreted as a date, even if anytime() was called. While convenient, it is also inconsistent as we otherwise take numeric values to be offsets to the epoch. Newer version are consistent: for anydate, a value is taken as date offset relative to the epoch (of January 1, 1970). For anytime, it is taken as seconds offset. So anytime(60) is one minute past the epoch, and anydate(60) is sixty days past it. The old behaviour can be enabled by setting the oldHeuristic argument to anytime (and utctime) to TRUE. Additionally, the default value can be set via getOption("anytimeOldHeuristic") which can be set to TRUE in startup file. Note that all other inputs such character, factor or ordered are not affected.

Warnings

As of version 0.3.10, a conversion from character resulting in a NA will lead to a warning being emitted. At most one warning per call is given: should numerous unparseable values be present on input, only one warning will be show. R offers mechanism to either suppress warnings, or convert them to errors as described in the help page for options() under the entry for warn.

References

This StackOverflow answer provided the initial idea: https://stackoverflow.com/a/3787188/143305.

See also

anytime-package, getFormats

Author

Dirk Eddelbuettel

Examples

## See the source code for a full list of formats, and the
## or the reference in help('anytime-package') for details
times <- c("2004-03-21 12:45:33.123456",
          "2004/03/21 12:45:33.123456",
          "20040321 124533.123456",
          "03/21/2004 12:45:33.123456",
          "03-21-2004 12:45:33.123456",
          "2004-03-21",
          "20040321",
          "03/21/2004",
          "03-21-2004",
          "20010101")
anytime(times)
#>  [1] "2004-03-21 12:45:33.123456 UTC" "2004-03-21 12:45:33.123456 UTC"
#>  [3] "2004-03-21 12:45:33.123456 UTC" "2004-03-21 12:45:33.123456 UTC"
#>  [5] "2004-03-21 12:45:33.123456 UTC" "2004-03-21 00:00:00.000000 UTC"
#>  [7] "2004-03-21 00:00:00.000000 UTC" "2004-03-21 00:00:00.000000 UTC"
#>  [9] "2004-03-21 00:00:00.000000 UTC" "2001-01-01 00:00:00.000000 UTC"
anydate(times)
#>  [1] "2004-03-21" "2004-03-21" "2004-03-21" "2004-03-21" "2004-03-21"
#>  [6] "2004-03-21" "2004-03-21" "2004-03-21" "2004-03-21" "2001-01-01"
utctime(times)
#>  [1] "2004-03-21 12:45:33.123456 UTC" "2004-03-21 12:45:33.123456 UTC"
#>  [3] "2004-03-21 12:45:33.123456 UTC" "2004-03-21 12:45:33.123456 UTC"
#>  [5] "2004-03-21 12:45:33.123456 UTC" "2004-03-21 00:00:00.000000 UTC"
#>  [7] "2004-03-21 00:00:00.000000 UTC" "2004-03-21 00:00:00.000000 UTC"
#>  [9] "2004-03-21 00:00:00.000000 UTC" "2001-01-01 00:00:00.000000 UTC"
utcdate(times)
#>  [1] "2004-03-21" "2004-03-21" "2004-03-21" "2004-03-21" "2004-03-21"
#>  [6] "2004-03-21" "2004-03-21" "2004-03-21" "2004-03-21" "2001-01-01"

## show effect of tz argument
anytime("2001-02-03 04:05:06")
#> [1] "2001-02-03 04:05:06 UTC"
## adjust parsed time to given TZ argument
anytime("2001-02-03 04:05:06", tz="America/Los_Angeles")
#> [1] "2001-02-02 20:05:06 PST"
## somewhat equvalent base R functionality
format(anytime("2001-02-03 04:05:06"), tz="America/Los_Angeles")
#> [1] "2001-02-02 20:05:06"