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Parsing: year-month-day

Source: R/gregorian-year-month-day.R
year_month_day_parse.Rd

year_month_day_parse() parses strings into a year-month-day.

The default options assume x should be parsed at day precision, using a format string of "%Y-%m-%d".

If a more precise precision than day is used, then time components will also be parsed. The default format separates date and time components by a "T" and the time components by a ":". For example, setting the precision to "second" will use a default format of "%Y-%m-%dT%H:%M:%S". This is aligned with the format() method for year-month-day, and with the RFC 3339 standard.

Usage

year_month_day_parse(
  x,
  ...,
  format = NULL,
  precision = "day",
  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.

precision

[character(1)]

A precision for the resulting year-month-day. One of:

  • "year"

  • "month"

  • "day"

  • "hour"

  • "minute"

  • "second"

  • "millisecond"

  • "microsecond"

  • "nanosecond"

Setting the precision determines how much information %S attempts to parse.

locale

[clock_locale]

A locale object created by clock_locale().

Value

A year-month-day calendar vector. If a parsing fails, NA is returned.

Details

year_month_day_parse() completely ignores the %z and %Z commands.

Full Precision Parsing

It is highly recommended to parse all of the information in the date-time string into a type at least as precise as the string. For example, if your string has fractional seconds, but you only require seconds, specify a sub-second precision, then round to seconds manually using whatever convention is appropriate for your use case. Parsing such a string directly into a second precision result is ambiguous and undefined, and is unlikely to work as you might expect.

Examples

x <- "2019-01-01"

# Default parses at day precision
year_month_day_parse(x)
#> <year_month_day<day>[1]>
#> [1] "2019-01-01"

# Can parse at less precise precisions too
year_month_day_parse(x, precision = "month")
#> <year_month_day<month>[1]>
#> [1] "2019-01"
year_month_day_parse(x, precision = "year")
#> <year_month_day<year>[1]>
#> [1] "2019"

# Even invalid dates can be round-tripped through format<->parse calls
invalid <- year_month_day(2019, 2, 30)
year_month_day_parse(format(invalid))
#> <year_month_day<day>[1]>
#> [1] "2019-02-30"

# Can parse with time of day
year_month_day_parse(
  "2019-01-30T02:30:00.123456789",
  precision = "nanosecond"
)
#> <year_month_day<nanosecond>[1]>
#> [1] "2019-01-30T02:30:00.123456789"

# Can parse using multiple format strings, which will be tried
# in the order they are provided
x <- c("2019-01-01", "2020-01-01", "2021/2/3")
formats <- c("%Y-%m-%d", "%Y/%m/%d")
year_month_day_parse(x, format = formats)
#> <year_month_day<day>[3]>
#> [1] "2019-01-01" "2020-01-01" "2021-02-03"

# Can parse using other format tokens as well
year_month_day_parse(
  "January, 2019",
  format = "%B, %Y",
  precision = "month"
)
#> <year_month_day<month>[1]>
#> [1] "2019-01"

# Parsing a French year-month-day
year_month_day_parse(
  "octobre 1, 2000",
  format = "%B %d, %Y",
  locale = clock_locale("fr")
)
#> <year_month_day<day>[1]>
#> [1] "2000-10-01"