get_n() not working for Date objects

[thibautjombart]

Hi there,

trying to test if a time interval is 'days' using get_n(), I get the following:

library(incidence2)
library(grates)
  
i <- rpois(100, lambda = exp(0.0523 * 1:100))
onset <- rep(Sys.Date() + 1:100, i)
incid <- incidence2::incidence(data.frame(onset), "onset")
dates <- get_dates(incid)
get_n(dates)
# Error in get_n.default() : Not implemented for class [Date].

It may be the desired behaviour, but if so it would be quite handy to restore a get_interval in incidence2.

[TimTaylor]

install_github("reconverse/incidence2/pkg") and then you have the following

i <- rpois(100, lambda = exp(0.0523 * 1:100))
onset <- rep(Sys.Date() + 1:100, i)
incid <- incidence2::incidence(data.frame(onset), "onset")
incidence2::get_interval_duration(incid)
#>  [1] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
#> [39] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
#> [77] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Is that sufficient?

[TimTaylor]

Can discuss tomorrow but the following is my motivation for being cautious about dates

i <- rpois(100, lambda = exp(0.0523 * 1:100))
onset <- rep(Sys.Date() + 1:100, i)
incid <- incidence2::incidence(data.frame(onset), "onset")
incidence2::get_interval_duration(incid)
#>  [1] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
#> [39] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
#> [77] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

onset2 <- onset + 0.1
incid2 <- incidence2::incidence(data.frame(onset2), "onset2")
#> Warning in incidence2::incidence(): Non-whole <Date> columns detected. These
#> can be confusing as they are displayed without the fractional element and can
#> also cause oddities when plotting. If you are interested in daily incidence,
#> consider removing the fractional part. This can be done prior to calling
#> `incidence()` or, alternatively, by setting the argument `interval = 'day'`
#> within the call itself.
incidence2::get_interval_duration(incid2)
#> Error in `get_interval_duration.incidence2()`:
#> ! Some values of 'date_index' are fractional dates so we cannot infer a duration.

[thibautjombart]

Thanks! I think it's great, but we can talk tomorrow. :)