clarify use of enw_retrospective_data

[sbfnk]

Aims to fix #79 with documentation and clearer argument names.

[seabbs]

So I looked at this a bit more and thought that maybe it would be better if enw_retrospective_data was split into two functions and standardised with enw_latest_data

Doing this gives the following workflow which personally I think is a little clearer and easier to use (much easier if allowing yourself to use some kind of pipe).

# Load epinowcast and data.table
library(epinowcast)
library(data.table)

# Load and filter germany hospitalisations
nat_germany_hosp <- germany_covid19_hosp[location == "DE"][age_group %in% "00+"]
nat_germany_hosp <- nat_germany_hosp[report_date <= as.Date("2021-10-01")]

# Make a retrospective dataset
retro_nat_germany <- nat_germany_hosp |>
  enw_filter_report_dates(remove_days = 40) |> 
  enw_filter_reference_dates(include_days = 40)

# Get latest observations for the same time period
latest_obs <- nat_germany_hosp |>
  enw_latest_data() |>
  enw_filter_report_dates(remove_days = 40) |> 
  enw_filter_reference_dates(include_days = 40)

The potential downside here is the duplication for retrospective and latest data but I think that might be hard to avoid.

Note: I haven't followed through fully with this idea yet (i.e tests, documentation updates, etc.) to avoid wasting work if we don't stick with this. Also yes this should probably be happening in another PR etc. etc. but sometimes we all have more ice cream than we should.

[codecov]

Codecov Report

Merging #82 (aca7847) into develop (68765e2) will increase coverage by 0.95%.
The diff coverage is 100.00%.

❗ Current head aca7847 differs from pull request most recent head 7f1a325. Consider uploading reports for the commit 7f1a325 to get more accurate results

@@             Coverage Diff             @@
##           develop      #82      +/-   ##
===========================================
+ Coverage    55.92%   56.88%   +0.95%     
===========================================
  Files           12       12              
  Lines          928      937       +9     
===========================================
+ Hits           519      533      +14     
+ Misses         409      404       -5     

Impacted Files	Coverage Δ
R/formula-tools.R	92.14% <ø> (ø)
R/check.R	68.42% <100.00%> (+68.42%)	⬆️
R/preprocess.R	94.38% <100.00%> (+2.49%)	⬆️
R/utils.R	65.71% <100.00%> (+3.21%)	⬆️

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