# Converting regional GDP data

## The `with_regions` argument

Use the `with_regions` argument in `convertGDP` to convert aggregated GDP data, e.g. regional-level data.

The default value is `NULL`, but if passed a data-frame with a country-to-region mapping, then custom regional codons will be recognized. The data-frame should have two columns, one named “iso3c” with iso3c country codes, and one named “region” with the corresponding region codes. The conversion of regional values is then undertaken by disaggregating the regions to a country level (using the mapping and weighed by the GDP (in $PPP) shares of countries within that region in the base year of `unit_in`).

    library(GDPuc)

    my_gdp <- tibble::tibble(
      iso3c = "EUR",
      year = 2010:2014,
      value = 100:104
    )

    my_mapping_data_frame <- tibble::tibble(
      iso3c = c("DEU", "FRA", "ESP", "ITA"),
      region = "EUR"
    )

    convertGDP(
      gdp = my_gdp,
      unit_in = "constant 2005 Int$PPP",
      unit_out = "constant 2017 Int$PPP",
      with_regions = my_mapping_data_frame,
      verbose = TRUE
    )
    #> ℹ Converting GDP with conversion factors from wb_wdi:
    #> constant 2005 Int$PPP → constant 2005 LCU
    #> 2005 PPP conversion factors in (LCU per international $) used:
    #> DEU: 0.872721
    #> ESP: 0.769508
    #> FRA: 0.916458
    #> ITA: 0.855139
    #> constant 2005 LCU → constant 2017 LCU
    #> 2017 value of base 2005 GDP deflators in (constant 2017 LCU per constant 2005
    #> LCU) used:
    #> DEU: 1.17792964301252
    #> ESP: 1.12733224080888
    #> FRA: 1.1473934842041
    #> ITA: 1.18510653093868
    #> constant 2017 LCU → constant 2017 Int$PPP
    #> 2017 PPP conversion factors in (LCU per international $) used:
    #> DEU: 0.744783
    #> ESP: 0.630839
    #> FRA: 0.770109
    #> ITA: 0.689895
    #> # A tibble: 5 × 3
    #>   iso3c  year value
    #>   <chr> <int> <dbl>
    #> 1 EUR    2010  140.
    #> 2 EUR    2011  141.
    #> 3 EUR    2012  142.
    #> 4 EUR    2013  144.
    #> 5 EUR    2014  145.