Counts the days from one date to another, both ends included, so the
result can be passed as the period length t to adp(),
admits(),
adpcnts() and
stkflow(). It saves getting
a fiscal year, a quarter or a leap year wrong by a day.
Arguments
- from
Start of the period: a single
Date, or a single valueas.Date()accepts (such as"2024-01-01"). Numbers are refused.- to
End of the period, inclusive, in the same forms; must not be before
from.
Value
A numeric scalar: the number of days in the period,
to - from + 1, for use as t. It has class
c("rmbl_perdays", "rmbl_measure", "numeric") and an attribute
"lakner" (from and to as dates), so it prints as a
box; arithmetic, round(), sum(), mean(),
[, c() and as.numeric() give a plain number, and
every t argument takes it as it is.
Details
Inclusive of both ends, because a period running from the 1st to the 31st is thirty-one days of exposure, not thirty. Leap years need no special handling: the arithmetic is on dates, so 2024 comes out at 366 and 2023 at 365 without anyone choosing.
Errors when either argument is numeric, has a length other than one, is
NA, or when to precedes from. Text that is not a
date fails inside as.Date() with base R's own message.
Examples
perdays("2024-01-01", "2024-12-31") # a leap year
#> ╭── Period length ──────────────────────────────────────────────────────╮
#> │ Length 366 days │
#> │ From 2024-01-01 │
#> │ To 2024-12-31 │
#> │ Formula t = to - from + 1 (both ends counted) │
#> │ │
#> │ From 2024-01-01 to 2024-12-31 is 366 days. │
#> │ Pass it as t to adp(), admits(), adpcnts() or stkflow(). │
#> │ │
#> │ Both ends count: the 1st to the 31st is 31 days of exposure. A leap │
#> │ year comes out at 366 from the dates, without anyone choosing. │
#> ╰───────────────────────────────────────────────────────────────────────╯
perdays("2023-01-01", "2023-12-31")
#> ╭── Period length ──────────────────────────────────────────────────────╮
#> │ Length 365 days │
#> │ From 2023-01-01 │
#> │ To 2023-12-31 │
#> │ Formula t = to - from + 1 (both ends counted) │
#> │ │
#> │ From 2023-01-01 to 2023-12-31 is 365 days. │
#> │ Pass it as t to adp(), admits(), adpcnts() or stkflow(). │
#> │ │
#> │ Both ends count: the 1st to the 31st is 31 days of exposure. A leap │
#> │ year comes out at 366 from the dates, without anyone choosing. │
#> ╰───────────────────────────────────────────────────────────────────────╯
perdays("2025-04-01", "2026-03-31") # a fiscal year
#> ╭── Period length ──────────────────────────────────────────────────────╮
#> │ Length 365 days │
#> │ From 2025-04-01 │
#> │ To 2026-03-31 │
#> │ Formula t = to - from + 1 (both ends counted) │
#> │ │
#> │ From 2025-04-01 to 2026-03-31 is 365 days. │
#> │ Pass it as t to adp(), admits(), adpcnts() or stkflow(). │
#> │ │
#> │ Both ends count: the 1st to the 31st is 31 days of exposure. A leap │
#> │ year comes out at 366 from the dates, without anyone choosing. │
#> ╰───────────────────────────────────────────────────────────────────────╯
# a quarter as the period of an average daily population
adp(4200, t = perdays(as.Date("2025-01-01"), as.Date("2025-03-31")))
#> ╭── Average daily population ─────────────────────────────────────────────╮
#> │ Average daily population 46.67 people on an average day │
#> │ Person-days 4,200 │
#> │ Period 90 days │
#> │ Formula adp = days / t = 4,200 / 90 │
#> │ │
#> │ 4,200 person-days over 90 days: 46.67 people held on an average day. │
#> │ │
#> │ Lakner (1976, p.15): a stock -- people held at once, not people who │
#> │ passed through. Count only the days served inside the period. │
#> │ adp = n x alos / t links it to alos() and admits(), exactly only in a │
#> │ steady state. │
#> ╰─────────────────────────────────────────────────────────────────────────╯
# numbers are not dates, and the end cannot come first
try(perdays(1, 31))
#> Error : `from` and `to` must be dates or date strings, not numbers
try(perdays("2024-12-31", "2024-01-01"))
#> Error : `to` must not precede `from`