These functions resolve messydates by their central tendency.
While the functions mean(), median(), and modal() expand all
elements of the vector into one combined set of dates and summarise it
to a single value (matching the usual behaviour of these generics),
the v*() versions resolve each element separately and so return a
vector of the same length as the input.
Usage
# S3 method for class 'mdate'
median(..., na.rm = TRUE)
vmedian(..., na.rm = TRUE)
# S3 method for class 'mdate'
vmedian(..., na.rm = TRUE)
# S3 method for class 'mdate'
mean(..., trim = 0, na.rm = TRUE)
vmean(..., na.rm = TRUE)
# S3 method for class 'mdate'
vmean(..., trim = 0, na.rm = TRUE)
modal(..., na.rm = TRUE)
# S3 method for class 'mdate'
modal(..., na.rm = TRUE)
vmodal(..., na.rm = TRUE)
# S3 method for class 'mdate'
vmodal(..., na.rm = TRUE)
random(..., na.rm = TRUE)
# S3 method for class 'mdate'
random(..., na.rm = TRUE)
vrandom(..., na.rm = TRUE)
# S3 method for class 'mdate'
vrandom(..., na.rm = TRUE)Details
All of these functions work by calling expand() to enumerate the
dates or date-times consistent with each messy value, then summarising
that expanded set. For median() and mean(), an even number of
expanded values is resolved by averaging the two middle values (via
POSIXct when a time of day is present, or Date otherwise); an odd
number simply returns the middle value.
Both kinds of set are expanded to their members and summarised the same
way, but the result means different things for each. For a {} ("all
members of") set, which records that something happened on several
dates, the central tendency describes where those occurrences sit. For a
[] ("one member of") set, which records that something happened on
exactly one of those dates but not which, the central tendency is a point
estimate of that single unknown date, as it is for a range or an
unspecified component. vrandom() draws a member uniformly in either
case, which for a [] set is a draw from the candidates themselves.
Averaging across the BCE/CE boundary, or between two BCE dates, is not
currently supported: median() falls back to the earlier of the two
middle values in that case, and mean()/vmean() may be unreliable for
solely negative-year inputs (a documented limitation, not a supported
feature).
Examples
d <- as_messydate(c("2008-03-25", "?2012-02-27", "2001-01?", "2001~",
"2001-01-01..2001-02-02", "{2001-01-01,2001-02-02}",
"{2001-01,2001-02-02}", "2008-XX-31", "-0050-01-01"))
d
#> 'mdate' chr [1:9] "2008-03-25" "?2012-02-27" "2001-01?" "~2001" ...
# the time of day is honoured when averaging precise date-times
r <- as_messydate(c("2012-06-01 09:00", "2012-06-01 17:00"))
median(r)
#> [1] "2012-06-01 13:00:00"
mean(r)
#> [1] "2012-06-01 13:00:00"
median(d)
#> [1] "2001-05-20"
vmedian(d)
#> [1] "2008-03-25" "2012-02-27" "2001-01-16" "2001-07-02" "2001-01-17"
#> [6] "2001-01-17" "2001-01-16" "2008-07-15" "-0050-01-01"
mean(d)
#> [1] "1997-07-15"
vmean(d)
#> [1] "2008-03-25" "2012-02-27" "2001-01-16" "2001-07-02" "2001-01-17"
#> [6] "2001-01-17" "2001-01-16" "2008-07-15" "50-01-01"
modal(d)
#> [1] "2001-01-01"
vmodal(d)
#> [1] "2008-03-25" "2012-02-27" "2001-01-01" "2001-01-01" "2001-01-01"
#> [6] "2001-01-01" "2001-01-01" "2008-01-31" "-0050-01-01"
random(d)
#> [1] "2001-01-09"
vrandom(d)
#> [1] "2008-03-25" "2012-02-27" "2001-01-05" "2001-12-24" "2001-01-31"
#> [6] "2001-02-02" "2001-01-06" "2008-09-30" "-0050-01-01"