RExpression support for nil tokens
Missing values support is being added to Kepler/Ptolemy by use of 'nil' values.
The RExpression actor needs to be able to handle 'nils' and convert to R 'NA'
#1 Updated by Dan Higgins over 15 years ago
RExpression actor has already been modified to handle nils on input ports. (This
occurs thru the use of a 'nil' -> 'NA' conversion based on string substitution
(since all input conversion is thru strings).
Currently (3/1/2005) conversion of output (NA -> nil) needs to be handled.