decimal form ICD-9 codes are not ambiguous if the leading zeroes are dropped.
Some short-form ICD-9 codes would not be ambiguous, e.g. "1" but many would
be problematic. This is the inverse of icd9_add_leading_zeroes.
icd9_drop_leading_zeroes(x, short_code = guess_short(x))icd9_drop_leading_zeroes_major(major)
is a character vector or factor of ICD-9 codes. If fewer than five characters is given in a code, then the digits are greedily assigned to hundreds, then tens, then units, before the decimal parts. E.g. "10" becomes "010", not "0010".
character vector of ICD-9 codes with extra zeroes dropped from major part
Invalid codes have no guaranteed result, and may give NA, or a (possibly valid) code in response.