Note that THIS FEATURE IS STILL EXPERIMENTAL: we strongly recommend checking a few converted dates manually. This function tries to extract dates from a character vector or a factor. It treats each entry independently, using regular expressions to detect if a date is present, its format, and if successful it converts that entry to a standard Date with the Ymd format (e.g. 2018-01-21). Entries which cannot be processed result in NA. An error threshold can be used to define the maximum number of resulting NA (i.e. entries without an identified date) that can be tolerated. If this threshold is exceeded, the original vector is returned.

guess_dates(
x,
error_tolerance = 0.1,
first_date = NULL,
last_date = Sys.Date(),
orders = getOption("linelist_guess_orders"),
quiet = TRUE,
modern_excel = TRUE
)

## Arguments

x a character vector or a factor a number between 0 and 1 indicating the proportion of entries which cannot be identified as dates to be tolerated; if this proportion is exceeded, the original vector is returned, and a message is issued; defaults to 0.1 (10 percent) a Date object specifying the first valid date. Defaults to fifty years before the last_date. a Date object specifying the last valid date. Defaults to the current date. date codes for fine-grained parsing of dates. This allows for parsing of mixed dates. If a list is supplied, that list will be used for successive tries in parsing. This is passed on to lubridate::parse_date_time(). Default orders (getOption("linelist_guess_orders")) parse World dmy/dby dates before US mdy/bdy dates. a logical indicating if messages should be displayed to the console (TRUE, default); set to FALSE to silence messages When parsing dates from excel, some dates are stored as integers. Modern versions of Excel represent dates as the number of days since 1900-01-01, but pre-2011 Excel for OSX have the origin set at 1904-01-01. If this parameter is TRUE (default), then this assumes that all numeric values represent dates from either a Windows version of Excel or a 2011 or later version of Excel for OSX. Set this parameter to FALSE if the data came from an OSX version of Excel before 2011.

## Details

Converting ambiguous character strings to dates is difficult for many reasons:

• dates may not use the standard Ymd format

• within the same variable, dates may follow different formats

• dates may be mixed with things that are not dates

• the behaviour of as.Date in the presence of non-date is hard to predict, sometimes returning NA, sometimes issuing an error.

This function tries to address all the above issues. Dates with the following format should be automatically detected, irrespective of separators (e.g. "-", " ", "/") and surrounding text:

• "19 09 2018"

• "2018 09 19"

• "19 Sep 2018"

• "2018 Sep 19"

• "Sep 19 2018"

### How it works

This function relies heavily on lubridate::parse_date_time(), which is an extremely flexible date parser that works well for consistent date formats, but can quickly become unweildy and may produce spurious results. guess_dates() will use a list of formats in the orders argument to run parse_date_time() with each format vector separately and take the first correctly parsed date from all the trials. By default, the orders are in getOption("linelist_guess_orders"):

list(
world_named_months = c("Ybd", "dby"),
world_digit_months = c("dmy", "Ymd"),
US_formats         = c("Omdy", "YOmd")
)


In this case, the dates 03 Jan 2018, 07/03/1982, and 08/20/85 are correctly intepreted as 2018-01-03, 1982-03-07, and 1985-08-20. The examples section will show how you can manipulate the orders to be customised for your situation.

clean_dates() for cleaning of data frames

## Examples


# Mixed format date -----------------------------------------

guess_dates(c("03 Jan 2018", "07/03/1982", "08/20/85")) # default#> [1] "2018-01-03" "1982-03-07" "1985-08-20"
# Prioritizing specific date formats ------------------------
#
# The default orders prioritize world date ordering over American-style.

print(ord <- getOption("linelist_guess_orders"))#> $world_named_months #> [1] "Ybd" "dby" #> #>$world_digit_months
#> [1] "dmy" "Ymd"
#>
#> $US_formats #> [1] "Omdy" "YOmd" #> # if you want to prioritize American-style dates with numeric months, you # can switch the second and third elements of the default orders print(ord <- getOption("linelist_guess_orders"))#>$world_named_months
#> [1] "Ybd" "dby"
#>
#> $world_digit_months #> [1] "dmy" "Ymd" #> #>$US_formats
#> [1] "Omdy" "YOmd"
#> print(us_ord <- ord[c(1, 3, 2)])#> $world_named_months #> [1] "Ybd" "dby" #> #>$US_formats
#> [1] "Omdy" "YOmd"
#>
#> $world_digit_months #> [1] "dmy" "Ymd" #> guess_dates(c("03 Jan 2018", "07/03/1982", "08/20/85"), orders = us_ord)#> [1] "2018-01-03" "1982-07-03" "1985-08-20" # Handling dates with time formats -------------------------- # # If you have a format with hours, minutes and seconds, you can also add that # to the list of formats. Note, however, that this function will drop levels # below day. print(ord$ymdhms <- c("Ymdhms", "Ymdhm"))#> [1] "Ymdhms" "Ymdhm"
guess_dates(c("2014_04_05_23:15:43", "03 Jan 2018", "07/03/1982", "08/20/85"), orders = ord)#> [1] "2014-04-05" "2018-01-03" "1982-03-07" "1985-08-20"
# Handling  missing and nonsense data -----------------------
#
# guess_dates can handle messy dates and tolerate missing data

x <- c("01-12-2001", "male", "female", "2018-10-18", NA, NA, "2018_10_17",
"43391", "2018 10 19", "// 24/12/1989", "this is 24/12/1989!",
"RECON NGO: 19 Sep 2018 :)", "6/9/11", "10/10/10")

guess_dates(x, error_tolerance = 1) # forced conversion#>  [1] "2001-12-01" NA           NA           "2018-10-18" NA
#>  [6] NA           "2018-10-17" "2018-10-18" "2018-10-19" "1989-12-24"
#> [11] "1989-12-24" "2018-09-19" "2011-09-06" "2010-10-10"
guess_dates(x, error_tolerance = 0.15) # only 15% errors allowed#>  [1] "01-12-2001"                "male"
#>  [3] "female"                    "2018-10-18"
#>  [5] NA                          NA
#>  [7] "2018_10_17"                "43391"
#>  [9] "2018 10 19"                "// 24/12/1989"
#> [11] "this is 24/12/1989!"       "RECON NGO: 19 Sep 2018 :)"
#> [13] "6/9/11"                    "10/10/10"