dbApply {RMySQL} | R Documentation |
Applies R 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.
dbApply(res, ...)
res |
a result set (see dbSendQuery ). |
... |
any additional arguments to be passed to FUN . |
dbApply
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 MySQL
driver implements a method
(see the helper function mysqlDBApply
) for this
generic function.
A list with as many elements as there were groups in the result set.
MySQL
mysqlDBApply
dbSendQuery
fetch
## Not run: ## compute quanitiles for each network agent con <- dbConnect(MySQL(), group="vitalAnalysis") 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)