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Parsing: zoned-time

Source: R/zoned-time.R
zoned-parsing.Rd

There are two parsers into a zoned-time, zoned_time_parse_complete() and zoned_time_parse_abbrev().

zoned_time_parse_complete()

zoned_time_parse_complete() is a parser for complete date-time strings, like "2019-01-01T00:00:00-05:00[America/New_York]". A complete date-time string has both the time zone offset and full time zone name in the string, which is the only way for the string itself to contain all of the information required to construct a zoned-time. Because of this, zoned_time_parse_complete() requires both the %z and %Z commands to be supplied in the format string.

The default options assume that x should be parsed at second precision, using a format string of "%Y-%m-%dT%H:%M:%S%Ez[%Z]". This matches the default result from calling format() on a zoned-time. Additionally, this format matches the de-facto standard extension to RFC 3339 for creating completely unambiguous date-times.

zoned_time_parse_abbrev()

zoned_time_parse_abbrev() is a parser for date-time strings containing only a time zone abbreviation, like "2019-01-01 00:00:00 EST". The time zone abbreviation is not enough to identify the full time zone name that the date-time belongs to, so the full time zone name must be supplied as the zone argument. However, the time zone abbreviation can help with resolving ambiguity around daylight saving time fallbacks.

For zoned_time_parse_abbrev(), %Z must be supplied and is interpreted as the time zone abbreviation rather than the full time zone name.

If used, the %z command must parse correctly, but its value will be completely ignored.

The default options assume that x should be parsed at second precision, using a format string of "%Y-%m-%d %H:%M:%S %Z". This matches the default result from calling print() or format(usetz = TRUE) on a POSIXct date-time.

Usage

zoned_time_parse_complete(
  x,
  ...,
  format = NULL,
  precision = "second",
  locale = clock_locale()
)

zoned_time_parse_abbrev(
  x,
  zone,
  ...,
  format = NULL,
  precision = "second",
  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 zoned-time. One of:

  • "second"

  • "millisecond"

  • "microsecond"

  • "nanosecond"

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

locale

[clock_locale]

A locale object created from clock_locale().

zone

[character(1)]

A full time zone name.

Value

A zoned-time.

Details

If zoned_time_parse_complete() is given input that is length zero, all NAs, or completely fails to parse, then no time zone will be able to be determined. In that case, the result will use "UTC".

If your date-time strings contain time zone offsets (like -04:00), but not the full time zone name, you might need sys_time_parse().

If your date-time strings don't contain time zone offsets or the full time zone name, you might need to use naive_time_parse(). From there, if you know the time zone that the date-times are supposed to be in, you can convert to a zoned-time with as_zoned_time().

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

library(magrittr)

zoned_time_parse_complete("2019-01-01T01:02:03-05:00[America/New_York]")
#> <zoned_time<second><America/New_York>[1]>
#> [1] "2019-01-01T01:02:03-05:00"

zoned_time_parse_complete(
  "January 21, 2019 -0500 America/New_York",
  format = "%B %d, %Y %z %Z"
)
#> <zoned_time<second><America/New_York>[1]>
#> [1] "2019-01-21T00:00:00-05:00"

# Nanosecond precision
x <- "2019/12/31 01:05:05.123456700-05:00[America/New_York]"
zoned_time_parse_complete(
  x,
  format = "%Y/%m/%d %H:%M:%S%Ez[%Z]",
  precision = "nanosecond"
)
#> <zoned_time<nanosecond><America/New_York>[1]>
#> [1] "2019-12-31T01:05:05.123456700-05:00"

# The `%z` offset must correspond to the true offset that would be used
# if the input was parsed as a naive-time and then converted to a zoned-time
# with `as_zoned_time()`. For example, the time that was parsed above used an
# offset of `-05:00`. We can confirm that this is correct with:
year_month_day(2019, 1, 1, 1, 2, 3) %>%
  as_naive_time() %>%
  as_zoned_time("America/New_York")
#> <zoned_time<second><America/New_York>[1]>
#> [1] "2019-01-01T01:02:03-05:00"

# So the following would not parse correctly
zoned_time_parse_complete("2019-01-01T01:02:03-04:00[America/New_York]")
#> Warning: Failed to parse 1 string at location 1. Returning `NA` at that location.
#> <zoned_time<second><America/New_York>[1]>
#> [1] NA

# `%z` is useful for breaking ties in otherwise ambiguous times. For example,
# these two times are on either side of a daylight saving time fallback.
# Without the `%z` offset, you wouldn't be able to tell them apart!
x <- c(
  "1970-10-25T01:30:00-04:00[America/New_York]",
  "1970-10-25T01:30:00-05:00[America/New_York]"
)

zoned_time_parse_complete(x)
#> <zoned_time<second><America/New_York>[2]>
#> [1] "1970-10-25T01:30:00-04:00" "1970-10-25T01:30:00-05:00"

# If you have date-time strings with time zone abbreviations,
# `zoned_time_parse_abbrev()` should be able to help. The `zone` must be
# provided, because multiple countries may use the same time zone
# abbreviation. For example:
x <- "1970-01-01 02:30:30 IST"

# IST = India Standard Time
zoned_time_parse_abbrev(x, "Asia/Kolkata")
#> <zoned_time<second><Asia/Kolkata>[1]>
#> [1] "1970-01-01T02:30:30+05:30"

# IST = Israel Standard Time
zoned_time_parse_abbrev(x, "Asia/Jerusalem")
#> <zoned_time<second><Asia/Jerusalem>[1]>
#> [1] "1970-01-01T02:30:30+02:00"

# The time zone abbreviation is mainly useful for resolving ambiguity
# around daylight saving time fallbacks. Without the abbreviation, these
# date-times would be ambiguous.
x <- c(
  "1970-10-25 01:30:00 EDT",
  "1970-10-25 01:30:00 EST"
)
zoned_time_parse_abbrev(x, "America/New_York")
#> <zoned_time<second><America/New_York>[2]>
#> [1] "1970-10-25T01:30:00-04:00" "1970-10-25T01:30:00-05:00"