icd9Condense: Condense ICD-9 code by replacing complete families with...
In jackwasey/icd9: Tools for Working with ICD-9 Codes, and Finding Comorbidities

This can be thought of as the inverse operation to icd9Children.

icd9Condense(icd9, isShort = icd9GuessIsShort(icd9), onlyReal = NULL,
  warn = TRUE)

icd9CondenseDecimal(icd9Decimal, onlyReal = NULL, warn = TRUE)

icd9CondenseShort(icd9Short, onlyReal = NULL, warn = TRUE,
  keepFactorLevels = FALSE)

`icd9`	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".
`isShort`	single logical value which determines whether the ICD-9 code provided is in short (TRUE) or decimal (FALSE) form. Where reasonable, this is guessed from the input data.
`onlyReal`	single logical value, if TRUE, will limit the search to those codes which appear in the master list, not just syntactically valid codes. Since nearly valid, out-dated or new codes may be missed, not limiting to 'real' values will be useful. Ultimately, there will need to be annual (and all-time) master lists of codes and the ability to test against a given master list given the year of the ICD-9 coding.
`warn`	single logical value, if `TRUE`, give warnings when there is discrepancy between `onlyReal` being `TRUE` yet data containing undefined codes.
`icd9Decimal`	character vector 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"
`icd9Short`	is a character vector 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"
`keepFactorLevels`	single logical value, default `FALSE`. If `TRUE`, will reuse the factor levels from the input data for the output data. This only applies if a factor is given for the input codes.