When searching for a way to transform characters to dates in R I came across this:
Why are my functions on lubridate dates so slow?
With the following code: fmt <- "%F", that is later used to specify the format 1984-04-21 in data.table::as.IDate(chr_dates, fmt).
Hence my question, since I expect to run into other cases like %F, sooner or later:
Is there a comprehensive list of Format Symbols and or a way to find definitions for such symbols inside R?
See help("strptime") (or here)
The details of the formats are platform-specific, but the following are likely to be widely available: most are defined by the POSIX standard. A conversion specification is introduced by %, usually followed by a single letter or O or E and then a single letter. Any character in the format string not part of a conversion specification is interpreted literally (and %% gives %). Widely implemented conversion specifications include
%a Abbreviated weekday name in the current locale on this platform. (Also matches full name on input: in some locales there are no abbreviations of names.)
%A Full weekday name in the current locale. (Also matches abbreviated name on input.)
%b Abbreviated month name in the current locale on this platform. (Also matches full name on input: in some locales there are no abbreviations of names.)
%B Full month name in the current locale. (Also matches abbreviated name on input.)
%c Date and time. Locale-specific on output, "%a %b %e %H:%M:%S %Y" on input.
%C Century (00–99): the integer part of the year divided by 100.
%d Day of the month as decimal number (01–31).
%D Date format such as %m/%d/%y: the C99 standard says it should be that exact format (but not all OSes comply).
%e Day of the month as decimal number (1–31), with a leading space for a single-digit number.
%F Equivalent to %Y-%m-%d (the ISO 8601 date format).
%g The last two digits of the week-based year (see %V). (Accepted but ignored on input.)
%G The week-based year (see %V) as a decimal number. (Accepted but ignored on input.)
%h Equivalent to %b.
%H Hours as decimal number (00–23). As a special exception strings such as ‘24:00:00’ are accepted for input, since ISO 8601 allows these.
%I Hours as decimal number (01–12).
%j Day of year as decimal number (001–366): For input, 366 is only valid in a leap year.
%m Month as decimal number (01–12).
%M Minute as decimal number (00–59).
%n Newline on output, arbitrary whitespace on input.
%p AM/PM indicator in the locale. Used in conjunction with %I and not with %H. An empty string in some locales (for example on some OSes, non-English European locales including Russia). The behaviour is undefined if used for input in such a locale. Some platforms accept %P for output, which uses a lower-case version (%p may also use lower case): others will output P.
%r For output, the 12-hour clock time (using the locale's AM or PM): only defined in some locales, and on some OSes misleading in locales which do not define an AM/PM indicator. For input, equivalent to %I:%M:%S %p.
%R Equivalent to %H:%M.
%S Second as integer (00–61), allowing for up to two leap-seconds (but POSIX-compliant implementations will ignore leap seconds).
%t Tab on output, arbitrary whitespace on input.
%T Equivalent to %H:%M:%S.
%u Weekday as a decimal number (1–7, Monday is 1). > %U Week of the year as decimal number (00–53) using Sunday as the first day 1 of the week (and typically with the first Sunday of the year as day 1 of week 1). The US convention.
%V Week of the year as decimal number (01–53) as defined in ISO 8601. If the week (starting on Monday) containing 1 January has four or more days in the new year, then it is considered week 1. Otherwise, it is the last week of the previous year, and the next week is week 1. See %G (%g) for the year corresponding to the week given by %V. (Accepted but ignored on input.)
%w Weekday as decimal number (0–6, Sunday is 0).
%W Week of the year as decimal number (00–53) using Monday as the first day of week (and typically with the first Monday of the year as day 1 of week 1). The UK convention.
%x Date. Locale-specific on output, "%y/%m/%d" on input.
%X Time. Locale-specific on output, "%H:%M:%S" on input.
%y Year without century (00–99). On input, values 00 to 68 are prefixed by 20 and 69 to 99 by 19 – that is the behaviour specified by the 2018 POSIX standard, but it does also say ‘it is expected that in a future version the default century inferred from a 2-digit year will change’.
%Y Year with century. Note that whereas there was no zero in the original Gregorian calendar, ISO 8601:2004 defines it to be valid (interpreted as 1BC): see https://en.wikipedia.org/wiki/0_(year). However, the standards also say that years before 1582 in its calendar should only be used with agreement of the parties involved. For input, only years 0:9999 are accepted.
%z Signed offset in hours and minutes from UTC, so -0800 is 8 hours behind UTC. (Standard only for output. For input R currently supports it on all platforms – values from -1400 to +1400 are accepted.)
%Z (Output only.) Time zone abbreviation as a character string (empty if not available). This may not be reliable when a time zone has changed abbreviations over the years.
Where leading zeros are shown they will be used on output but are optional on input. Names are matched case-insensitively on input: whether they are capitalized on output depends on the platform and the locale. Note that abbreviated names are platform-specific (although the standards specify that in the ‘C’ locale they must be the first three letters of the capitalized English name: this convention is widely used in English-language locales but for example the French month abbreviations are not the same on any two of Linux, macOS, Solaris and Windows). Knowing what the abbreviations are is essential if you wish to use %a, %b or %h as part of an input format: see the examples for how to check.
When %z or %Z is used for output with an object with an assigned time zone an attempt is made to use the values for that time zone — but it is not guaranteed to succeed.
The definition of ‘whitespace’ for %n and %t is platform-dependent: for most it does not include non-breaking spaces.
Not in the standards and less widely implemented are
%k The 24-hour clock time with single digits preceded by a blank.
%l The 12-hour clock time with single digits preceded by a blank.