Null values in the Aster Database are typically mapped to an "NA" value in the R environment. However, the Aster Database environment passes null values as either the value "NULL" or as empty strings.
To instruct the Aster Database to replace null values with "NA" before passing them to the R environment, users can use the NULLSTRING argument of the Stream Teradata Aster SQL-MapReduce® function, which allows users to use any value as a replacement for null values before they are passed to the R environment. Likewise, the Aster Database recognizes values given in the NULLSTRING argument as NULL values in data returned from the R environment.
For more information about the handling of null values, refer to "Stream Function Usage" in the Teradata Aster® Developer Guide.