rmongodb: substract date in aggregation

Question

After finally figuring out how to parameterize an aggregation pipeline with a date using mongo.bson.from.list() , I've been wrangling with the snippet below to get the $min for the date difference below, but keep getting

 Error in mongo.aggregation(m, collection , aggregation_pipeline ) : 
   mongoDB error: 10. Please check ?mongo.get.err for more details.

which means that my BSON group expression, although acceptable to mongo.bson.from.list() , is rejected by mongo.aggregation() .

I've tried using list() rather than c() , and cod rather than its ISODate definition, with various quoting variations.

 cod <- as.POSIXct("2015-01-01 00:00:00" , tz = "GMT" )

 grouparg_bson1 <- mongo.bson.from.list(
   list( '$group' = list( '_id'     = list('ID'        = '$dcmt.cid') ,
                          'dtdiff'  = list('$min'      = list('$subtract' = c('$dcmt.orddt','ISODate("2015-01-01T00:00:00Z")' )) ),
                          'tota'    = list('$sum'      = '$dcmt.A' ),
                          'list'    = list('$addToSet' = '$dcmt.B' )
   ))
 )

I am using mongo's latest stable release, version 3.2.4.

Answer 1

Trial & error: the following works.

 grouparg_bson1 <- mongo.bson.from.list(
   list( '$group' = list( '_id'     = list('ID'        = '$dcmt.cid') ,
                          'dtdiff'  = list('$min'      = list('$subtract' = list('$dcmt.orddt', cod )) ),
                          'tota'    = list('$sum'      = '$dcmt.A' ),
                          'list'    = list('$addToSet' = '$dcmt.B' )
   ))
 )