Attempts to detect and clean up suspected ZIP codes. Will strip "ZIP+4" suffixes to match format of zipcode data.frame. Restores leading zeros, converts invalid entries to NAs, and returns character vector. Note that this function does not attempt to find a matching ZIP code in the database, but rather examines formatting alone.
This package contains a database of city, state, latitude, and longitude information for U.S. ZIP codes from the CivicSpace Database (August 2004) and augmented by Daniel Coven's federalgovernmentzipcodes.us web site (updated January 22, 2012). Previous versions of this package (before 1.0) were based solely on the CivicSpace data, so an original version of the CivicSpace database is also included.
providing 
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