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README.md

parsedate — Parse dates from ISO 8601, and guess the format

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This R package has three functions for dealing with dates.

  • parse_iso_8601 recognizes and parses all valid ISO 8601 date and time formats. It can also be used as an ISO 8601 validator.
  • parse_date can parse a date when you don't know which format it is in. First it tries all ISO 8601 formats. Then it tries git's versatile date parser. Lastly, it tries as.POSIXct.
  • format_iso_8601 formats a date (and time) in specific ISO 8601 format.

Limitations

The git parser does not work for dates before 1970 and after 2100. For these dates the current year is used instead:

parse_date("april 15 1971")
## Error in parse_date("april 15 1971"): could not find function "parse_date"
parse_date("april 15 1969")
## Error in parse_date("april 15 1969"): could not find function "parse_date"
parse_date("april 15 2110")
## Error in parse_date("april 15 2110"): could not find function "parse_date"

Parsing ISO 8601 dates

parse_iso_8601 recognizes all valid ISO 8601 formats, and gives an NA for invalid dates. Here are some examples

Dates with missing fields

library(parsedate)
parse_iso_8601("2013-02-08 09")
## [1] "2013-02-08 09:00:00 UTC"
parse_iso_8601("2013-02-08 09:30")
## [1] "2013-02-08 09:30:00 UTC"

Separator between date and time

parse_iso_8601("2013-02-08T09")
## [1] "2013-02-08 09:00:00 UTC"
parse_iso_8601("2013-02-08T09:30")
## [1] "2013-02-08 09:30:00 UTC"
parse_iso_8601("2013-02-08T09:30:26")
## [1] "2013-02-08 09:30:26 UTC"

Fractional seconds, minutes, hours

parse_iso_8601("2013-02-08T09:30:26.123")
## [1] "2013-02-08 09:30:26 UTC"
parse_iso_8601("2013-02-08T09:30.5")
## [1] "2013-02-08 09:30:30 UTC"
parse_iso_8601("2013-02-08T09,25")
## [1] "2013-02-08 09:15:00 UTC"

Zulu time zone is UTC

parse_iso_8601("2013-02-08T09:30:26Z")
## [1] "2013-02-08 09:30:26 UTC"

ISO weeks are parsed properly

parse_iso_8601("2013-W06-5")
## [1] "2013-02-08 UTC"
parse_iso_8601("2013-W01-1")
## [1] "2012-12-31 UTC"
parse_iso_8601("2009-W01-1")
## [1] "2008-12-29 UTC"
parse_iso_8601("2009-W53-7")
## [1] "2010-01-03 UTC"

Day of the year

parse_iso_8601("2013-039")
## [1] "2013-02-08 UTC"
parse_iso_8601("2013-039 09:30:26Z")
## [1] "2013-02-08 09:30:26 UTC"

Guess the format of the date, and parse it

Sometimes one has to work with a large number of dates, in arbitrary formats. It is of impossible to reliably guess the format of some dates, because of ambiguity. But it is often not critical to get the date exactly right in the ambiguous cases, and this is when the parse_date function is useful. It tries a large number of formats, here is the algorithm is uses:

  1. Try parsing dates using all valid ISO 8601 formats, by calling parse_iso_8601.
  2. If this fails, then try parsing them using the git date parser.
  3. If this fails, then try parsing them using as.POSIXct. (It is unlikely that this step will parse any dates that the first two steps couldn't, but it is still a logical fallback, to make sure that we can parse at least as many dates as as.POSIXct.

Here are some examples. The first ones are easy.

parse_date("2014-12-12")
## [1] "2014-12-12 UTC"
parse_date("04/15/99")
## [1] "1999-04-15 UTC"
parse_date("15/04/99")
## [1] "1999-04-15 UTC"

Ambiguous formats

The following formats are ambiguous and are parsed as month/day/year.

parse_date("12/11/99")
## [1] "1999-12-11 UTC"
parse_date("11/12/99")
## [1] "1999-11-12 UTC"

Fill in the current date and time for missing fields

parse_date("03/20")
## [1] "2019-03-20 UTC"
parse_date("12")
## [1] "2019-05-12 UTC"

But not for this, because this is ISO 8601.

parse_date("2014")
## [1] "2014-01-01 UTC"

Formatting dates as ISO 8601

The format_iso_8601 function formats a date (and time) in a fixed format that is ISO 8601 valid, and can be used to compare dates as character strings. It converts the date(s) to UTC.

format_iso_8601(parse_iso_8601("2013-02-08"))
## [1] "2013-02-08T00:00:00+00:00"
format_iso_8601(parse_iso_8601("2013-02-08 09:34:00"))
## [1] "2013-02-08T09:34:00+00:00"
format_iso_8601(parse_iso_8601("2013-02-08 09:34:00+01:00"))
## [1] "2013-02-08T08:34:00+00:00"
format_iso_8601(parse_iso_8601("2013-W06-5"))
## [1] "2013-02-08T00:00:00+00:00"
format_iso_8601(parse_iso_8601("2013-039"))
## [1] "2013-02-08T00:00:00+00:00"

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R package to parse dates given in arbitrary formats

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