Applies R/S-Plus functions to groups of remote DBMS rows without bringing an entire result set all at once. The result set is expected to be sorted by the grouping field.
This generic is meant to handle somewhat gracefully(?) large amounts
of data from the DBMS by bringing into R manageable chunks;
the idea is that the data from individual groups can be handled by R, but
not all the groups at the same time.
Currently, only the
PostgreSQL driver implements a method
(see the helper function
postgresqlDBApply) for this
A list with as many elements as there were groups in the result set.
1 2 3 4 5 6 7 8 9
## Not run: ## compute quantiles for each network agent con <- dbConnect(PostgreSQL(), user= "user", password="passwd", dbname="sample") rs <- dbSendQuery(con, "select Agent, ip_addr, DATA from pseudo_data order by Agent") out <- dbApply(rs, INDEX = "Agent", FUN = function(x, grp) quantile(x$DATA, names=FALSE)) ## End(Not run)
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