parse_date_time: Parse character and numeric date-time vectors with user friendly order formats.

Description

parse_date_time parses an input vector into POSIXct date-time object. It differs from strptime in two respects. First, it allows specification of the order in which the formats occur without the need to include separators and "%" prefix. Such a formating argument is refered 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 as strptime.

Usage

parse_date_time(x, orders, tz = "UTC", truncated = 0, quiet = FALSE,
  locale = Sys.getlocale("LC_TIME"), select_formats = .select_formats,
  exact = FALSE)
parse_date_time2(x, orders, tz = "UTC", exact = FALSE)
fast_strptime(x, format, tz = "UTC")

Arguments

a character or numeric vector of dates

orders

a character vector of date-time formats. Each order string is series of formatting characters as listed strptime but might not include the "%" prefix, for example "ymd" will match all the possible date

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 truncated parameter is non-zero parse_date_time also

quiet

logical. When TRUE progress messages are not printed, and "no formats found" error is surpresed and the function simply returns a vector of NAs. This mirrors the behavior of base R functions strptime and as.POSIXct. Default is F

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 orde

exact

logical. If TRUE, orders parameter is interpreted as an exact strptime format and no trainign or guessing are performed.

format

a character string of formats. It should include all the separators and each format must be prefixed withargument of strptime.

Value

a vector of POSIXct date-time objects

Details

When several format-orders are specified parse_date_time sorts the supplied format-orders based on a training set and then applies them recursively on the input vector.

parse_date_time, and hence all the derived functions, such as ymd_hms, ymd etc, will drop into fast_strptime instead of strptime whenever the guesed from the input data formats are all numeric.

The list below contains formats recognized by lubridate. For numeric formats leading 0s are optional. In contrast to strptime, some of the formats have been extended for efficiency reasons. They are marked with "*". Fast perasers, parse_date_time2 and fast_strptime, currently accept only formats marked with "!".

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Examples

Run this code

## ** 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"

## ** heterogenuous 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)
parse_date_time(x, "ymd_hms", truncated = 3)
## [1] "2011-12-31 12:59:59 UTC" "2010-01-01 12:11:00 UTC"
## [3] "2010-01-01 12:00:00 UTC" "2010-01-01 00:00:00 UTC"

## ** 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)
## [1] "2001-09-01 00:00:00 UTC" "2002-09-01 00:00:00 UTC" NA "2003-09-01 12:02:00 UT
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)
## [1] "1996-12-17 04:00:00 UTC" "1950-04-18 01:30:00 UTC"

## ** fast parsing **
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)

## ** how to use `select_formats` argument **
## By default \%Y has precedence:
parse_date_time(c("27-09-13", "27-09-2013"), "dmy")
## [1] "13-09-27 UTC"   "2013-09-27 UTC"

## to give priority to \%y format, define your own select_format function:

my_select <-   function(trained){
   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)
## '[1] "2013-09-27 UTC" "2013-09-27 UTC"

Run the code above in your browser using DataLab

Get 50% off unlimited learning