Feature request: more options for filtering database during creation

[joelnitta]

Currently, the only options for limiting the size of the database are:

1. preselection argument of db_download(), which allows for selection of GenBank "division" (i.e., plant, bacterial, invertebrate, etc)
2. min_length argument of db_create()
3. max_length argument of db_create()

This does not work well if someone is only interested in a clade (e.g., ferns) within one of the larger divisions (e.g., plants; ca. 800gb), as the local database is much larger than needed and therefore slow.

So what I propose is a way to limit the database during creation by ID (i.e., GenBank accession number). This is very similar to the example given for extracting data from the database, but instead of returning data to R, it would reduce the size of the external database created. That way, future queries would run on a smaller database and go faster.

Another idea would be to limit the database by taxonomic level, but I am not sure if that is possible with the information available during parsing of the files downloaded from GenBank.