get_ssp_regions: get_ssp_regions
In rohmin9122/gcam-korea-release: Build the GCAM-Korea Input Datasets

Get regions for different income groups in SSP4 2010 (by default)

1 2	get_ssp_regions(pcGDP, reg_names, income_group, ssp_filter = "SSP4", year_filter = 2010)

`pcGDP`	A tibble with per capita GDP estimates, including columns `GCAM_region_ID`, `scenario`, `year`, and `value`
`reg_names`	A tibble with columns `GCAM_region_ID` and `region`
`income_group`	A string indicating which region group (low, medium, high)
`ssp_filter`	A string indicating which SSP to filter to (SSP4 by default)
`year_filter`	An integer indicating which year to use (2010 by default)