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# stri_datetime_format: Date and Time Formatting and Parsing

## Description

These functions convert a given date/time object to a character vector, or vice versa.

## Usage

    stri_datetime_format(
      time,
      format = "uuuu-MM-dd HH:mm:ss",
      tz = NULL,
      locale = NULL
    )

    stri_datetime_parse(
      str,
      format = "uuuu-MM-dd HH:mm:ss",
      lenient = FALSE,
      tz = NULL,
      locale = NULL
    )

## Arguments

`time` | an object of class `POSIXct` with date-time data to be formatted (`as.POSIXct` will be called on character vectors and objects of class `POSIXlt`, `Date`, and `factor`)
`format` | character vector, see Details; see also `stri_datetime_fstr`
`tz` | `NULL` or `''` for the default time zone or a single string with a timezone identifier, see `stri_timezone_get` and `stri_timezone_list`
`locale` | `NULL` or `''` for the default locale, or a single string with locale identifier; a non-Gregorian calendar may be specified by setting the `@calendar=name` keyword
`str` | character vector with strings to be parsed
`lenient` | single logical value; should date/time parsing be lenient?

## Details

Vectorized over `format` and `time` or `str`.

When parsing strings, unspecified date-time fields (e.g., seconds where only hours and minutes are given) are based on today’s midnight in the local time zone (for compatibility with `strptime`).

By default, `stri_datetime_format` (for compatibility with the `strftime` function) formats a date/time object using the current default time zone.

`format` may be one of `DT_STYLE` or `DT_relative_STYLE`, where `DT` is equal to `date`, `time`, or `datetime`, and `STYLE` is equal to `full`, `long`, `medium`, or `short`. This gives a locale-dependent date and/or time format. Note that currently ICU does not support `relative` `time` formats, thus this flag is currently ignored in such a context.

Otherwise, `format` is a pattern: a string where specific sequences of characters are replaced with date/time data from a calendar when formatting or used to generate data for a calendar when parsing. For example, `y` stands for ‘year’. Characters may be used multiple times: `yy` might produce `99`, whereas `yyyy` yields `1999`. For most numerical fields, the number of characters specifies the field width. For example, if `h` is the hour, `h` might produce `5`, but `hh` yields `05`. For some characters, the count specifies whether an abbreviated or full form should be used.

Two single quotes represent a literal single quote, either inside or outside single quotes. Text within single quotes is not interpreted in any way (except for two adjacent single quotes). Otherwise, all ASCII letters from `a` to `z` and `A` to `Z` are reserved as syntax characters, and require quoting if they are to represent literal characters. In addition, certain ASCII punctuation characters may become available in the future (e.g., `:` being interpreted as the time separator and `/` as a date separator, and replaced by respective locale-sensitive characters in display).

Symbol | Meaning | Example(s) | Output
G | era designator | G, GG, or GGG | AD
|  | GGGG | Anno Domini
|  | GGGGG | A
y | year | yy | 96
|  | y or yyyy | 1996
u | extended year | u | 4601
U | cyclic year name, as in Chinese lunar calendar | U |
r | related Gregorian year | r | 1996
Q | quarter | Q or QQ | 02
|  | QQQ | Q2
|  | QQQQ | 2nd quarter
|  | QQQQQ | 2
q | Stand Alone quarter | q or qq | 02
|  | qqq | Q2
|  | qqqq | 2nd quarter
|  | qqqqq | 2
M | month in year | M or MM | 09
|  | MMM | Sep
|  | MMMM | September
|  | MMMMM | S
L | Stand Alone month in year | L or LL | 09
|  | LLL | Sep
|  | LLLL | September
|  | LLLLL | S
w | week of year | w or ww | 27
W | week of month | W | 2
d | day in month | d | 2
|  | dd | 02
D | day of year | D | 189
F | day of week in month | F | 2 (2nd Wed in July)
g | modified Julian day | g | 2451334
E | day of week | E, EE, or EEE | Tue
|  | EEEE | Tuesday
|  | EEEEE | T
|  | EEEEEE | Tu
e | local day of week | e or ee | 2
| example: if Monday is 1st day, Tuesday is 2nd ) | eee | Tue
|  | eeee | Tuesday
|  | eeeee | T
|  | eeeeee | Tu
c | Stand Alone local day of week | c or cc | 2
|  | ccc | Tue
|  | cccc | Tuesday
|  | ccccc | T
|  | cccccc | Tu
a | am/pm marker | a | pm
h | hour in am/pm (1~12) | h | 7
|  | hh | 07
H | hour in day (0~23) | H | 0
|  | HH | 00
k | hour in day (1~24) | k | 24
|  | kk | 24
K | hour in am/pm (0~11) | K | 0
|  | KK | 00
m | minute in hour | m | 4
|  | mm | 04
s | second in minute | s | 5
|  | ss | 05
S | fractional second - truncates (like other time fields) | S | 2
| to the count of letters when formatting. Appends | SS | 23
| zeros if more than 3 letters specified. Truncates at | SSS | 235
| three significant digits when parsing. | SSSS | 2350
A | milliseconds in day | A | 61201235
z | Time Zone: specific non-location | z, zz, or zzz | PDT
|  | zzzz | Pacific Daylight Time
Z | Time Zone: ISO8601 basic hms? / RFC 822 | Z, ZZ, or ZZZ | -0800
| Time Zone: long localized GMT (=OOOO) | ZZZZ | GMT-08:00
| Time Zone: ISO8601 extended hms? (=XXXXX) | ZZZZZ | -08:00, -07:52:58, Z
O | Time Zone: short localized GMT | O | GMT-8
| Time Zone: long localized GMT (=ZZZZ) | OOOO | GMT-08:00
v | Time Zone: generic non-location | v | PT
| (falls back first to VVVV) | vvvv | Pacific Time or Los Angeles Time
V | Time Zone: short time zone ID | V | uslax
| Time Zone: long time zone ID | VV | America/Los_Angeles
| Time Zone: time zone exemplar city | VVV | Los Angeles
| Time Zone: generic location (falls back to OOOO) | VVVV | Los Angeles Time
X | Time Zone: ISO8601 basic hm?, with Z for 0 | X | -08, +0530, Z
| Time Zone: ISO8601 basic hm, with Z | XX | -0800, Z
| Time Zone: ISO8601 extended hm, with Z | XXX | -08:00, Z
| Time Zone: ISO8601 basic hms?, with Z | XXXX | -0800, -075258, Z
| Time Zone: ISO8601 extended hms?, with Z | XXXXX | -08:00, -07:52:58, Z
x | Time Zone: ISO8601 basic hm?, without Z for 0 | x | -08, +0530
| Time Zone: ISO8601 basic hm, without Z | xx | -0800
| Time Zone: ISO8601 extended hm, without Z | xxx | -08:00
| Time Zone: ISO8601 basic hms?, without Z | xxxx | -0800, -075258
| Time Zone: ISO8601 extended hms?, without Z | xxxxx | -08:00, -07:52:58
‘ | escape for text | ‘ | (nothing)
‘ ‘ | two single quotes produce one | ‘ ‘ | ‘

Note that any characters in the pattern that are not in the ranges of `[a-z]` and `[A-Z]` will be treated as quoted text. For instance, characters like `:`, `.`, (a space), `#` and `@` will appear in the resulting time text even if they are not enclosed within single quotes. The single quote is used to “escape” the letters. Two single quotes in a row, inside or outside a quoted sequence, represent a “real” single quote.

A few examples:

Example Pattern | Result
yyyy.MM.dd ‘at’ HH:mm:ss zzz | 2015.12.31 at 23:59:59 GMT+1
EEE, MMM d, ‘’yy | czw., gru 31, ‘15
h:mm a | 11:59 PM
hh ‘o’’clock’ a, zzzz | 11 o’clock PM, GMT+01:00
K:mm a, z | 11:59 PM, GMT+1
yyyyy.MMMM.dd GGG hh:mm aaa | 2015.grudnia.31 n.e. 11:59 PM
uuuu-MM-dd’T’HH:mm:ssZ | 2015-12-31T23:59:59+0100 (the ISO 8601 guideline)

## Value

`stri_datetime_format` returns a character vector.

`stri_datetime_parse` returns an object of class `POSIXct`.

## Author(s)

Marek Gagolewski and other contributors

## References

Formatting Dates and Times – ICU User Guide, https://unicode-org.github.io/icu/userguide/format_parse/datetime/

## See Also

The official online manual of stringi at https://stringi.gagolewski.com/

Gagolewski M., stringi: Fast and portable character string processing in R, Journal of Statistical Software 103(2), 2022, 1-59, doi:10.18637/jss.v103.i02

Other datetime: `stri_datetime_add()`, `stri_datetime_create()`, `stri_datetime_fields()`, `stri_datetime_fstr()`, `stri_datetime_now()`, `stri_datetime_symbols()`, `stri_timezone_get()`, `stri_timezone_info()`, `stri_timezone_list()`

## Examples

    x <- c('2015-02-28', '2015-02-29')
    stri_datetime_parse(x, 'yyyy-MM-dd')
    ## [1] "2015-02-28 CET" NA
    stri_datetime_parse(x, 'yyyy-MM-dd', lenient=TRUE)
    ## [1] "2015-02-28 CET" "2015-03-01 CET"
    stri_datetime_parse(x %s+% " 17:13", "yyyy-MM-dd HH:mm")
    ## [1] "2015-02-28 17:13:00 CET" NA
    stri_datetime_parse('19 lipca 2015', 'date_long', locale='pl_PL')
    ## [1] "2015-07-19 CEST"
    stri_datetime_format(stri_datetime_now(), 'datetime_relative_medium')
    ## [1] "today, 12:31:06 PM"