Hi, all
I've noticed that as.Date can't be applied to Spark data frame. I've created 
the following UDF and used dapply to change a integer column "aa"  to a date 
with origin as 1960-01-01.
change_date<-function(df){   df<-as.POSIXlt(as.Date(df$aa, origin = 
"1960-01-01", tz = "UTC"))   } customSchema<- structType(structField("rc", 
"integer"),   ....   structField("change_date(x)","timestamp"))
rollup_1_t <- dapply(rollup_1, function(x) { x <- 
It works with a small dataset but it takes forever to finish on a big dataset. 
It does not give a result when I used 'head(rollup_1_t).
 I guess it is because for "change_date" function, it converts the spark data 
frame back to R data frame, which is slow and would potentially fail. Is there 
a better solution?

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