list_spdf_regions_with_data: Creates a vector of values (typically locations) in a spatial...
In dr9593/automapper:

The function will look at a spatial dataframe and the source dataframe that was merged into it, and, will return a vector of unique values where data in the source dataframe existed. For example, if data was represented in the source dataframe at the community-level and then joined with the spatial dataframe, and the region_to_subset_by column is governorate, this will return a vector of governorates where data from the source dataframe exists. This is particularly useful for subsetting and facetting maps, not over an entire country, but focusing only on regions where data was collected.

1 2	list_spdf_regions_with_data(spatial_dataframe, source_dataframe, spatial_key, df_key, region_to_subset_by)

`spatial_dataframe`	The spatial dataframe to be subsetted
`source_dataframe`	The dataframe that was merged into the spatial dataframe
`spatial_key`	The column name in the spatial object's dataframe (accessed by spatial_layer@data) that was used to join the two dataframes.
`region_to_subset_by`	The column name in the spatial_dataframe you want to filter by. For example, the column representing the governorate-level in a map, so you only keep governorates where communities exist where data was collected.
`dataframe_key`	The column name in the dataframe to be used as a key to join with the spatial data. that was used as a key to join the spatial datawith the dataframe.