 This function is a simple helper to calculate the total number of pages of an article.

## Usage

``jst_get_total_pages(first_page, last_page, page_range, quietly = FALSE)``

## Arguments

first_page

The first page of an article (numeric).

last_page

The last page of an article (numeric).

page_range

The page range of an article (character).

quietly

Sometimes page ranges contain roman numerals like `xiv`. These are not recognized, return `NA` and raise a warning. If set to `TRUE`, this warning not raised.

## Value

A vector with the calculated total pages.

## Details

This function deals with four cases:

• if all three arguments are missing, NA is returned.

• if page_range is supplied, the number of pages is calculated from it.

• if only the first page is supplied, NA is returned.

• if first and last page are supplied, the number of pages is calculated as `last_page - first_page + 1`.

The algorithm to parse page ranges works as follows: A typical page range is `1-10, 200` where the article starts at page 1, ends at page 10, and has an erratum at page 200. For this case, the range is calculated as `range + single_page`, as in`(10 - 1 + 1) + 1 = 11`. Sometimes multiple ranges are given: `1-10, 11-20`. For those cases all ranges are summed: `(10 - 1 + 1) + (20 - 11 + 1) = 20`. Another specification for multiple ranges is `1-10+11-20`, which is treated similarly.

## Examples

``````# calculate pages from first and last page
first_pages <- sample(30:50, 10)
last_pages <- first_pages + sample(5:20, 10)
page_ranges <- rep(NA_character_, 10)

jst_get_total_pages(first_pages, last_pages, page_ranges)
#>   19 10 18 11  6 13  8 17 12 14

# get pages from page range
jst_get_total_pages(NA_real_, NA_real_, "51 - 70")
#>  20
jst_get_total_pages(NA_real_, NA_real_, "51 - 70, 350")
#>  21
jst_get_total_pages(NA_real_, NA_real_, "350, 51 - 70")
#>  21
jst_get_total_pages(NA_real_, NA_real_, "51 - 70, 80-100")
#>  41
jst_get_total_pages(NA_real_, NA_real_, "51-70+350")
#>  21
``````