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Parsing: date

Source: R/date.R
date_parse.Rd

date_parse() parses strings into a Date.

The default format used is "%Y-%m-%d". This matches the default result from calling print() or format() on a Date.

Usage

date_parse(x, ..., format = NULL, locale = clock_locale())

Arguments

x

[character]

A character vector to parse.

...

These dots are for future extensions and must be empty.

format

[character / NULL]

A format string. A combination of the following commands, or NULL, in which case a default format string is used.

A vector of multiple format strings can be supplied. They will be tried in the order they are provided.

Year

  • %C: The century as a decimal number. The modified command %NC where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 2. Leading zeroes are permitted but not required.

  • %y: The last two decimal digits of the year. If the century is not otherwise specified (e.g. with %C), values in the range [69 - 99] are presumed to refer to the years [1969 - 1999], and values in the range [00 - 68] are presumed to refer to the years [2000 - 2068]. The modified command %Ny, where N is a positive decimal integer, specifies the maximum number of characters to read. If not specified, the default is 2. Leading zeroes are permitted but not required.

  • %Y: The year as a decimal number. The modified command %NY where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 4. Leading zeroes are permitted but not required.

Month

  • %b, %B, %h: The locale's full or abbreviated case-insensitive month name.

  • %m: The month as a decimal number. January is 1. The modified command %Nm where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 2. Leading zeroes are permitted but not required.

Day

  • %d, %e: The day of the month as a decimal number. The modified command %Nd where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 2. Leading zeroes are permitted but not required.

Day of the week

  • %a, %A: The locale's full or abbreviated case-insensitive weekday name.

  • %w: The weekday as a decimal number (0-6), where Sunday is 0. The modified command %Nw where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 1. Leading zeroes are permitted but not required.

ISO 8601 week-based year

  • %g: The last two decimal digits of the ISO week-based year. The modified command %Ng where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 2. Leading zeroes are permitted but not required.

  • %G: The ISO week-based year as a decimal number. The modified command %NG where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 4. Leading zeroes are permitted but not required.

  • %V: The ISO week-based week number as a decimal number. The modified command %NV where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 2. Leading zeroes are permitted but not required.

  • %u: The ISO weekday as a decimal number (1-7), where Monday is 1. The modified command %Nu where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 1. Leading zeroes are permitted but not required.

Week of the year

  • %U: The week number of the year as a decimal number. The first Sunday of the year is the first day of week 01. Days of the same year prior to that are in week 00. The modified command %NU where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 2. Leading zeroes are permitted but not required.

  • %W: The week number of the year as a decimal number. The first Monday of the year is the first day of week 01. Days of the same year prior to that are in week 00. The modified command %NW where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 2. Leading zeroes are permitted but not required.

Day of the year

  • %j: The day of the year as a decimal number. January 1 is 1. The modified command %Nj where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 3. Leading zeroes are permitted but not required.

Date

  • %D, %x: Equivalent to %m/%d/%y.

  • %F: Equivalent to %Y-%m-%d. If modified with a width (like %NF), the width is applied to only %Y.

Time of day

  • %H: The hour (24-hour clock) as a decimal number. The modified command %NH where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 2. Leading zeroes are permitted but not required.

  • %I: The hour (12-hour clock) as a decimal number. The modified command %NI where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 2. Leading zeroes are permitted but not required.

  • %M: The minutes as a decimal number. The modified command %NM where N is a positive decimal integer specifies the maximum number of characters to read. If not specified, the default is 2. Leading zeroes are permitted but not required.

  • %S: The seconds as a decimal number. Leading zeroes are permitted but not required. If encountered, the locale determines the decimal point character. Generally, the maximum number of characters to read is determined by the precision that you are parsing at. For example, a precision of "second" would read a maximum of 2 characters, while a precision of "millisecond" would read a maximum of 6 (2 for the values before the decimal point, 1 for the decimal point, and 3 for the values after it). The modified command %NS, where N is a positive decimal integer, can be used to exactly specify the maximum number of characters to read. This is only useful if you happen to have seconds with more than 1 leading zero.

  • %p: The locale's equivalent of the AM/PM designations associated with a 12-hour clock. The command %I must precede %p in the format string.

  • %R: Equivalent to %H:%M.

  • %T, %X: Equivalent to %H:%M:%S.

  • %r: Equivalent to %I:%M:%S %p.

Time zone

  • %z: The offset from UTC in the format [+|-]hh[mm]. For example -0430 refers to 4 hours 30 minutes behind UTC. And 04 refers to 4 hours ahead of UTC. The modified command %Ez parses a : between the hours and minutes and leading zeroes on the hour field are optional: [+|-]h[h][:mm]. For example -04:30 refers to 4 hours 30 minutes behind UTC. And 4 refers to 4 hours ahead of UTC.

  • %Z: The full time zone name or the time zone abbreviation, depending on the function being used. A single word is parsed. This word can only contain characters that are alphanumeric, or one of '_', '/', '-' or '+'.

Miscellaneous

  • %c: A date and time representation. Equivalent to %a %b %d %H:%M:%S %Y.

  • %%: A % character.

  • %n: Matches one white space character. %n, %t, and a space can be combined to match a wide range of white-space patterns. For example "%n " matches one or more white space characters, and "%n%t%t" matches one to three white space characters.

  • %t: Matches zero or one white space characters.

locale

[clock_locale]

A locale object created from clock_locale().

Value

A Date.

Details

date_parse() ignores both the %z and %Z commands, as clock treats Date as a naive type, with a yet-to-be-specified time zone.

Parsing strings with sub-daily components, such as hours, minutes, or seconds, should generally be done with date_time_parse(). If you only need the date components from a string with sub-daily components, choose one of the following:

  • If the date components are at the front of the string, and you don't want the time components to affect the date in any way, you can use date_parse() to parse only the date components. For example, date_parse("2019-01-05 00:01:02", format = "%Y-%m-%d") will parse through 05 and then stop.

  • If you want the time components to influence the date, then parse the full string with date_time_parse(), round to day precision with a rounding function like date_round(), and cast to date with as_date().

Attempting to directly parse all components of a sub-daily string into a Date is ambiguous and undefined, and is unlikely to work as you might expect. For example, date_parse("2019-01-05 00:01:02", format = "%Y-%m-%d %H:%M:%S") is not officially supported, even if it works in some cases.

Examples

date_parse("2020-01-01")
#> [1] "2020-01-01"

date_parse(
  "January 5, 2020",
  format = "%B %d, %Y"
)
#> [1] "2020-01-05"

# With a different locale
date_parse(
  "janvier 5, 2020",
  format = "%B %d, %Y",
  locale = clock_locale("fr")
)
#> [1] "2020-01-05"

# A neat feature of `date_parse()` is the ability to parse
# the ISO year-week-day format
date_parse("2020-W01-2", format = "%G-W%V-%u")
#> [1] "2019-12-31"

# ---------------------------------------------------------------------------
# Sub-daily components

# If you have a string with sub-daily components, but only require the date,
# first parse them as date-times to fully parse the sub-daily components,
# then round using whatever convention is required for your use case before
# converting to date.
x <- c("2019-01-01 11", "2019-01-01 12")

x <- date_time_parse(x, zone = "UTC", format = "%Y-%m-%d %H")
x
#> [1] "2019-01-01 11:00:00 UTC" "2019-01-01 12:00:00 UTC"

date_floor(x, "day")
#> [1] "2019-01-01 UTC" "2019-01-01 UTC"
date_round(x, "day")
#> [1] "2019-01-01 UTC" "2019-01-02 UTC"

as_date(date_round(x, "day"))
#> [1] "2019-01-01" "2019-01-02"