name_to_abbr: Get state abbreviations from state names
Description
Look up state abbreviations by state names (including District of Columbia
and Puerto Rico); this function is based on grep(), and hence allows for
regular expressions.
A vector of state abbreviations if ties_method equals "first", and
a list of state abbreviations otherwise.
Arguments
name
Vector of state names 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.