icd9df
data frame containing columns for visitId (which is the feault
name), icd9 (default for the icd9 code), and maybe also a POA flag.
icd9Field
The column in the data frame which contains the ICD codes.
This is a character vector of length one. If it is NULL
, icd9
will attempt to guess the column name, looking for progressively less
likely possibilities until it matche a single column. Failing this, it will
take the first column in the data frame. Specifying the column using this
argument avoids the guesswork.