ICD-9 codes are represented in short and decimal forms. The short form has up to 5 digits, or V or E followed by up to four digits. The decimal form has a decimal point to delimit the top-level (henceforth major) category, and the minor part containing the subsidiary classifications.
For conversions of ICD-9 or ICD-10 codes between the short and
decimal forms, use short_to_decimal and
decimal_to_short.
icd does not covert ICD-9 to ICD-10 codes yet.
Other ICD code conversion: as.icd_long_data,
long_to_wide, wide_to_long