parse_date_time
User friendly date-time parsing functions
parse_date_time()
parses an input vector into POSIXct date-time
object. It differs from base::strptime()
in two respects. First,
it allows specification of the order in which the formats occur without the
need to include separators and the %
prefix. Such a formatting argument is
referred to as "order". Second, it allows the user to specify several
format-orders to handle heterogeneous date-time character
representations.
parse_date_time2()
is a fast C parser of numeric
orders.
fast_strptime()
is a fast C parser of numeric formats only
that accepts explicit format arguments, just like
base::strptime()
.
- Keywords
- chron
Usage
parse_date_time(
x,
orders,
tz = "UTC",
truncated = 0,
quiet = FALSE,
locale = Sys.getlocale("LC_TIME"),
select_formats = .select_formats,
exact = FALSE,
train = TRUE,
drop = FALSE
)parse_date_time2(
x,
orders,
tz = "UTC",
exact = FALSE,
lt = FALSE,
cutoff_2000 = 68L
)
fast_strptime(x, format, tz = "UTC", lt = TRUE, cutoff_2000 = 68L)
Arguments
- x
a character or numeric vector of dates
- orders
a character vector of date-time formats. Each order string is a series of formatting characters as listed in
base::strptime()
but might not include the"%"
prefix. For example, "ymd" will match all the possible dates in year, month, day order. Formatting orders might include arbitrary separators. These are discarded. See details for implemented formats.- tz
a character string that specifies the time zone with which to parse the dates
- truncated
integer, number of formats that can be missing. The most common type of irregularity in date-time data is the truncation due to rounding or unavailability of the time stamp. If the
truncated
parameter is non-zeroparse_date_time()
also checks for truncated formats. For example, if the format order is "ymdHMS" andtruncated = 3
,parse_date_time()
will correctly parse incomplete date-times like2012-06-01 12:23
,2012-06-01 12
and2012-06-01
. NOTE: Theymd()
family of functions is based onbase::strptime()
which currently fails to parse%Y-%m
formats.- quiet
logical. If
TRUE
, progress messages are not printed, andNo formats found
error is suppressed and the function simply returns a vector of NAs. This mirrors the behavior of base R functionsbase::strptime()
andbase::as.POSIXct()
.- locale
locale to be used, see locales. On Linux systems you can use
system("locale -a")
to list all the installed locales.- select_formats
A function to select actual formats for parsing from a set of formats which matched a training subset of
x
. It receives a named integer vector and returns a character vector of selected formats. Names of the input vector are formats (not orders) that matched the training set. Numeric values are the number of dates (in the training set) that matched the corresponding format. You should use this argument if the default selection method fails to select the formats in the right order. By default the formats with most formatting tokens (%
) are selected and%Y
counts as 2.5 tokens (so that it has a priority over%y%m
). See examples.- exact
logical. If
TRUE
, theorders
parameter is interpreted as an exactbase::strptime()
format and no training or guessing are performed (i.e.train
,drop
parameters are irrelevant).- train
logical, default
TRUE
. Whether to train formats on a subset of the input vector. The result of this is that supplied orders are sorted according to performance on this training set, which commonly results in increased performance. Please note that even whentrain = FALSE
(andexact = FALSE
) guessing of the actual formats is still performed on a pseudo-random subset of the original input vector. This might result inAll formats failed to parse
error. See notes below.- drop
logical, default
FALSE
. Whether to drop formats that didn't match on the training set. IfFALSE
, unmatched on the training set formats are tried as a last resort at the end of the parsing queue. Applies only whentrain = TRUE
. Setting this parameter toTRUE
might slightly speed up parsing in situations involving many formats. Prior to v1.7.0 this parameter was implicitlyTRUE
, which resulted in occasional surprising behavior when rare patterns where not present in the training set.- lt
logical. If
TRUE
, returned object is of class POSIXlt, and POSIXct otherwise. For compatibility withbase::strptime()
the default isTRUE
forfast_strptime()
andFALSE
forparse_date_time2()
.- cutoff_2000
integer. For
y
format, two-digit numbers smaller or equal tocutoff_2000
are parsed as 20th's century, 19th's otherwise. Available only for functions relying onlubridate
s internal parser.- format
a character string of formats. It should include all the separators and each format must be prefixed with %, just as in the format argument of
base::strptime()
.
Details
When several format-orders are specified, parse_date_time()
selects
(guesses) format-orders based on a training subset of the input
strings. After guessing the formats are ordered according to the performance
on the training set and applied recursively on the entire input vector. You
can disable training with train = FALSE
.
parse_date_time()
, and all derived functions, such as ymd_hms()
,
ymd()
, etc., will drop into fast_strptime()
instead of
base::strptime()
whenever the guessed from the input data formats are all
numeric.
The list below contains formats recognized by lubridate. For numeric formats
leading 0s are optional. As compared to base::strptime()
, some of the
formats are new or have been extended for efficiency reasons. These formats
are marked with "(*)". The fast parsers parse_date_time2()
and
fast_strptime()
accept only formats marked with "(!)".
a
Abbreviated weekday name in the current locale. (Also matches full name)
A
Full weekday name in the current locale. (Also matches abbreviated name).
You don't need to specify
a
andA
formats explicitly. Wday is automatically handled ifpreproc_wday = TRUE
b
(!)Abbreviated or full month name in the current locale. The C parser currently understands only English month names.
B
(!)Same as b.
d
(!)Day of the month as decimal number (01--31 or 0--31)
H
(!)Hours as decimal number (00--24 or 0--24).
I
(!)Hours as decimal number (01--12 or 1--12).
j
Day of year as decimal number (001--366 or 1--366).
q
(!*)Quarter (1--4). The quarter month is added to the parsed month if
m
format is present.m
(!*)Month as decimal number (01--12 or 1--12). For
parse_date_time
. As a lubridate extension, also matches abbreviated and full months names asb
andB
formats. C parser understands only English month names.M
(!)Minute as decimal number (00--59 or 0--59).
p
(!)AM/PM indicator in the locale. Normally used in conjunction with
I
and not withH
. But the lubridate C parser accepts H format as long as hour is not greater than 12. C parser understands only English locale AM/PM indicator.S
(!)Second as decimal number (00--61 or 0--61), allowing for up to two leap-seconds (but POSIX-compliant implementations will ignore leap seconds).
OS
Fractional second.
U
Week of the year as decimal number (00--53 or 0--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.
w
Weekday as decimal number (0--6, Sunday is 0).
W
Week of the year as decimal number (00--53 or 0--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.
y
(!*)Year without century (00--99 or 0--99). In
parse_date_time()
also matches year with century (Y format).Y
(!)Year with century.
z
(!*)ISO8601 signed offset in hours and minutes from UTC. For example
-0800
,-08:00
or-08
, all represent 8 hours behind UTC. This format also matches the Z (Zulu) UTC indicator. Becausebase::strptime()
doesn't fully support ISO8601 this format is implemented as an union of 4 orders: Ou (Z), Oz (-0800), OO (-08:00) and Oo (-08). You can use these four orders as any other but it is rarely necessary.parse_date_time2()
andfast_strptime()
support all of the timezone formats.Om
(!*)Matches numeric month and English alphabetic months (Both, long and abbreviated forms).
Op
(!*)Matches AM/PM English indicator.
r
(*)Matches
Ip
andH
orders.R
(*)Matches
HM
andIMp
orders.T
(*)Matches
IMSp
,HMS
, andHMOS
orders.
Value
a vector of POSIXct date-time objects
Note
parse_date_time()
(and the derivatives ymd()
, ymd_hms()
, etc.)
relies on a sparse guesser that takes at most 501 elements from the supplied
character vector in order to identify appropriate formats from the
supplied orders. If you get the error All formats failed to parse
and
you are confident that your vector contains valid dates, you should either
set exact
argument to TRUE
or use functions that don't perform format
guessing (fast_strptime()
, parse_date_time2()
or base::strptime()
).
For performance reasons, when timezone is not UTC,
parse_date_time2()
and fast_strptime()
perform no validity checks for
daylight savings time. Thus, if your input string contains an invalid date
time which falls into DST gap and lt = TRUE
you will get an POSIXlt
object with a non-existent time. If lt = FALSE
your time instant will be
adjusted to a valid time by adding an hour. See examples. If you want to
get NA for invalid date-times use fit_to_timeline()
explicitly.
See Also
Examples
# NOT RUN {
## ** orders are much easier to write **
x <- c("09-01-01", "09-01-02", "09-01-03")
parse_date_time(x, "ymd")
parse_date_time(x, "y m d")
parse_date_time(x, "%y%m%d")
# "2009-01-01 UTC" "2009-01-02 UTC" "2009-01-03 UTC"
## ** heterogeneous date-times **
x <- c("09-01-01", "090102", "09-01 03", "09-01-03 12:02")
parse_date_time(x, c("ymd", "ymd HM"))
## ** different ymd orders **
x <- c("2009-01-01", "02022010", "02-02-2010")
parse_date_time(x, c("dmY", "ymd"))
## "2009-01-01 UTC" "2010-02-02 UTC" "2010-02-02 UTC"
## ** truncated time-dates **
x <- c("2011-12-31 12:59:59", "2010-01-01 12:11", "2010-01-01 12", "2010-01-01")
parse_date_time(x, "Ymd HMS", truncated = 3)
## ** specifying exact formats and avoiding training and guessing **
parse_date_time(x, c("%m-%d-%y", "%m%d%y", "%m-%d-%y %H:%M"), exact = TRUE)
parse_date_time(c('12/17/1996 04:00:00','4/18/1950 0130'),
c('%m/%d/%Y %I:%M:%S','%m/%d/%Y %H%M'), exact = TRUE)
## ** quarters and partial dates **
parse_date_time(c("2016.2", "2016-04"), orders = "Yq")
parse_date_time(c("2016", "2016-04"), orders = c("Y", "Ym"))
## ** fast parsing **
# }
# NOT RUN {
options(digits.secs = 3)
## random times between 1400 and 3000
tt <- as.character(.POSIXct(runif(1000, -17987443200, 32503680000)))
tt <- rep.int(tt, 1000)
system.time(out <- as.POSIXct(tt, tz = "UTC"))
system.time(out1 <- ymd_hms(tt)) # constant overhead on long vectors
system.time(out2 <- parse_date_time2(tt, "YmdHMOS"))
system.time(out3 <- fast_strptime(tt, "%Y-%m-%d %H:%M:%OS"))
all.equal(out, out1)
all.equal(out, out2)
all.equal(out, out3)
# }
# NOT RUN {
## ** how to use `select_formats` argument **
## By default %Y has precedence:
parse_date_time(c("27-09-13", "27-09-2013"), "dmy")
## to give priority to %y format, define your own select_format function:
my_select <- function(trained, drop=FALSE, ...){
n_fmts <- nchar(gsub("[^%]", "", names(trained))) + grepl("%y", names(trained))*1.5
names(trained[ which.max(n_fmts) ])
}
parse_date_time(c("27-09-13", "27-09-2013"), "dmy", select_formats = my_select)
## ** invalid times with "fast" parsing **
parse_date_time("2010-03-14 02:05:06", "YmdHMS", tz = "America/New_York")
parse_date_time2("2010-03-14 02:05:06", "YmdHMS", tz = "America/New_York")
parse_date_time2("2010-03-14 02:05:06", "YmdHMS", tz = "America/New_York", lt = TRUE)
# }