abbr_to_name: Get state names from state abbreviations
Description
Look up state names by state abbreviations (including District of Columbia
and Puerto Rico); this function is based on grep(), and hence allows for
regular expressions.
A vector of state names if ties_method equals "first", and a list
of state names otherwise.
Arguments
abbr
Vector of state abbreviations to look up.
ignore.case, perl, fixed
Arguments to pass to grep(), with the same
defaults as in the latter function. Hence, by default, regular expressions
are used; to match against a fixed string (no regular expressions), set
fixed = TRUE.
ties_method
If "first", then only the first match for each name is
returned. If "all", then all matches for each name are returned.