## Derive/Impute a Date from a Date Character Vector

### Description

Derive a date ('--DT') from a date character vector (⁠'--DTC⁠'). The date can be imputed (see date_imputation argument) and the date imputation flag ('⁠--DTF'⁠) can be added.

### Usage

derive_vars_dt(
dataset,
new_vars_prefix,
dtc,
highest_imputation = "n",
date_imputation = "first",
flag_imputation = "auto",
min_dates = NULL,
max_dates = NULL,
preserve = FALSE
)


### Arguments

 dataset Input dataset. The date character vector (dtc) must be present. new_vars_prefix Prefix used for the output variable(s). A character scalar is expected. For the date variable "DT" is appended to the specified prefix and for the date imputation flag "DTF". I.e., for new_vars_prefix = "AST" the variables ASTDT and ASTDTF are created. dtc The '--DTC' date to impute A character date is expected in a format like yyyy-mm-dd or yyyy-mm-ddThh:mm:ss. Trailing components can be omitted and - is a valid "missing" value for any component. highest_imputation Highest imputation level The highest_imputation argument controls which components of the DTC value are imputed if they are missing. All components up to the specified level are imputed. If a component at a higher level than the highest imputation level is missing, NA_character_ is returned. For example, for highest_imputation = "D" "2020" results in NA_character_ because the month is missing. If "n" is specified no imputation is performed, i.e., if any component is missing, NA_character_ is returned. If "Y" is specified, date_imputation should be "first" or "last" and min_dates or max_dates should be specified respectively. Otherwise, NA_character_ is returned if the year component is missing. Default: "n" Permitted Values: "Y" (year, highest level), "M" (month), "D" (day), "n" (none, lowest level) date_imputation The value to impute the day/month when a datepart is missing. A character value is expected, either as a format with month and day specified as "mm-dd": e.g. "06-15" for the 15th of June (The year can not be specified; for imputing the year "first" or "last" together with min_dates or max_dates argument can be used (see examples).), or as a keyword: "first", "mid", "last" to impute to the first/mid/last day/month. The argument is ignored if highest_imputation is less then "D". Default: "first" flag_imputation Whether the date imputation flag must also be derived. If "auto" is specified, the date imputation flag is derived if the date_imputation argument is not null. Default: "auto" Permitted Values: "auto", "date" or "none" min_dates Minimum dates A list of dates is expected. It is ensured that the imputed date is not before any of the specified dates, e.g., that the imputed adverse event start date is not before the first treatment date. Only dates which are in the range of possible dates of the dtc value are considered. The possible dates are defined by the missing parts of the dtc date (see example below). This ensures that the non-missing parts of the dtc date are not changed. A date or date-time object is expected. For example impute_dtc_dtm( "2020-11", min_dates = list( ymd_hms("2020-12-06T12:12:12"), ymd_hms("2020-11-11T11:11:11") ), highest_imputation = "M" )  returns "2020-11-11T11:11:11" because the possible dates for "2020-11" range from "2020-11-01T00:00:00" to "2020-11-30T23:59:59". Therefore "2020-12-06T12:12:12" is ignored. Returning "2020-12-06T12:12:12" would have changed the month although it is not missing (in the dtc date). max_dates Maximum dates A list of dates is expected. It is ensured that the imputed date is not after any of the specified dates, e.g., that the imputed date is not after the data cut off date. Only dates which are in the range of possible dates are considered. A date or date-time object is expected. preserve Preserve day if month is missing and day is present For example "2019---07" would return ⁠"2019-06-07⁠ if preserve = TRUE (and date_imputation = "MID"). Permitted Values: TRUE, FALSE Default: FALSE

### Details

In admiral we don't allow users to pick any single part of the date/time to impute, we only enable to impute up to a highest level, i.e. you couldn't choose to say impute months, but not days.

The presence of a '--DTF' variable is checked and if it already exists in the input dataset, a warning is issued and '--DTF' will be overwritten.

### Value

The input dataset with the date '--DT' (and the date imputation flag '--DTF' if requested) added.

### Author(s)

Samia Kabi

Date/Time Derivation Functions that returns variable appended to dataset: derive_var_trtdurd(), derive_vars_dtm_to_dt(), derive_vars_dtm_to_tm(), derive_vars_dtm(), derive_vars_duration(), derive_vars_dy()

### Examples

library(tibble)
library(lubridate)

mhdt <- tribble(
~MHSTDTC,
"2019-07-18T15:25:40",
"2019-07-18T15:25",
"2019-07-18",
"2019-02",
"2019",
"2019---07",
""
)

# Create ASTDT and ASTDTF
# No imputation for partial date
derive_vars_dt(
mhdt,
new_vars_prefix = "AST",
dtc = MHSTDTC
)

# Create ASTDT and ASTDTF
# Impute partial dates to first day/month
derive_vars_dt(
mhdt,
new_vars_prefix = "AST",
dtc = MHSTDTC,
highest_imputation = "M"
)

# Impute partial dates to 6th of April
derive_vars_dt(
mhdt,
new_vars_prefix = "AST",
dtc = MHSTDTC,
highest_imputation = "M",
date_imputation = "04-06"
)

# Create AENDT and AENDTF
# Impute partial dates to last day/month
derive_vars_dt(
mhdt,
new_vars_prefix = "AEN",
dtc = MHSTDTC,
highest_imputation = "M",
date_imputation = "last"
)

# Create BIRTHDT
# Impute partial dates to 15th of June. No DTF
derive_vars_dt(
mhdt,
new_vars_prefix = "BIRTH",
dtc = MHSTDTC,
highest_imputation = "M",
date_imputation = "mid",
flag_imputation = "none"
)

# Impute AE start date to the first date and ensure that the imputed date
# is not before the treatment start date
~AESTDTC, ~TRTSDTM,
"2020-12", ymd_hms("2020-12-06T12:12:12"),
"2020-11", ymd_hms("2020-12-06T12:12:12")
)

derive_vars_dt(
dtc = AESTDTC,
new_vars_prefix = "AST",
highest_imputation = "M",
min_dates = vars(TRTSDTM)
)

# A user imputing dates as middle month/day, i.e. date_imputation = "mid" can
# use preserve argument to "preserve" partial dates.  For example, "2019---07",
# will be displayed as "2019-06-07" rather than 2019-06-15 with preserve = TRUE

derive_vars_dt(
mhdt,
new_vars_prefix = "AST",
dtc = MHSTDTC,
highest_imputation = "M",
date_imputation = "mid",
preserve = TRUE
)