Transition (version 1.0.1)

PreviousDate: Find Previous Test Date for Subject

Description

get_prev_dates() identifies the previous test date for individual subjects and timepoints in a longitudinal study.

add_prev_date() interpolates these previous test dates into a data frame for further analysis.

Usage

add_prev_date(
  object,
  subject = "subject",
  timepoint = "timepoint",
  result = "result",
  prev_date = "prev_date"
)
get_prev_date(
  object,
  subject = "subject",
  timepoint = "timepoint",
  result = "result"
)

Value

add_prev_date()

A data.frame based on object, with an added column named as specified by argument prev_date of class Date containing the values of the previous test dates.

get_prev_date()

An vector of length nrow(object), class Date, containing the values of the previous test dates ordered in the exact sequence of the subject and timepoint in object.

Arguments

object

a data.frame (or object coercible by as.data.frame() to a data frame) containing the data to be analysed.

subject

character, name of the column (of type integer or factor) identifying individual study subjects; default "subject".

timepoint

character, name of the column recording time points (as Dates) of testing of subjects; default "timepoint".

result

character, name of the column (of type ordered factor, or binary, see Details) recording test results; default "result".

prev_date

character, name to be used for a new column to record previous test dates; default "prev_date".

Details

See Transitions details.

See Also

data.frame, Dates, ordered factor.

Other transitions: PreviousResult, Transitions, uniques()

Examples

# \dontshow{
Blackmore <- transform(Blackmore, timepoint = as.Date("2000-01-01") + round(age * 365.25),
    result = cut(exercise, breaks = seq(0, 30, 2), labels = paste0("<=", seq(0, 30, 2)[-1]),
        include.lowest = TRUE, ordered_result = TRUE))
# }

 ## Continuing example from `add_transitions()`
  # subject, timepoint and result arguments all defaults and required types
Blackmore |> str()

  # Integer vector of the previous test dates
get_prev_date(Blackmore)

  # Add column of  previous test dates to data frame
add_prev_date(Blackmore) |> head(32)

rm(Blackmore)

###
## Example on formatting numeric values as R dates

#  Data frame containing year as numeric: 2018 to 2025
(df <- data.frame(
    subject = rep(1001:1003),
    timepoint = rep(2018:2025, each = 3),
    result = gl(3, 4, lab = c("jolly", "good", "show"), ordered = TRUE)
    ))

#  Convert to R dates
df <- transform(df,
           timepoint = as.Date(paste(timepoint, "01", "01", sep = "-"))
      )

  # Add column of test result transitions (defaults: cap = 0, modulate = 0)
(df <- add_transitions(df))

# Format R dates just to show the year
transform(df, timepoint = format(timepoint, "%Y"))

#  Data frame containing year and month as numeric: July 2024 to June 2025
(df <- data.frame(
           subject = 1001:1002,
           year = rep(2024:2025, each = 12),
           month = rep(c(7:12, 1:6), each = 2),
           result = gl(2, 3, lab = c("low", "high"), ordered = TRUE)
       ))

#  Convert to R dates
df <- transform(df, timepoint = as.Date(paste(year, month, "01", sep = "-")))
# \dontshow{
    df$year <- NULL
    df$month <- NULL
# }

  # Add column of test result transitions (defaults: cap = 0, modulate = 0)
(df <- add_transitions(df))

# Format R dates just to show the month and year
transform(df, timepoint = format(timepoint, "%b-%Y"))

rm(df)