I’m guessing you can do this in C++, but hey… it works for me.

You’ll notice 3 functions that need to be created, the main function which will be called from Vertica, the params functions which is optional and holds the config of parameters optionally pased to the function. And finally, and mandatory, is the factory function which tells Vertica what to expect when running ‘group_concat’.

group_concat <- function(x,y) {

 options(useFancyQuotes=FALSE)

 # initialize parameters
 sep <- ifelse(is.null(y[['delimiter']]),',',as.character(y[['delimiter']]))
 if(is.null(y[['quote']])) y[['quote']] <- 0
 doQuote <- ifelse(y[['quote']]==1 ,TRUE,FALSE) 

 if(doQuote) ret <- paste0(sQuote(x[,1]),collapse=sep)
 else ret <- paste0(x[,1],collapse=sep)

 ret

}

group_concat_params <- function() {
 params <- data.frame(datatype=c("varchar", "int"), length=c(100,NA), scale=rep(NA,2),name=c("delimiter","quote"))
 params
}

group_concat_factory <- function() {
 list(
 name=group_concat
 ,udxtype=c("transform")
 ,intype=c("any")
 ,outtype=c("varchar(65000)")
 ,parametertypecallback=group_concat_params
 # ,volatility=c("stable")
 # ,strict=c("called_on_null_input")
 )
}

After distributiong the file into the same directory on all nodes.

In Vertica run :

create or replace library r_func as '.../group_concat.r' language 'R';
create or replace transform function group_concat as name 'group_concat_factory' library r_func;

select group_concat(id using parameters delimiter='|', quote=1) over() from sometable;