datashield.aggregate {DSI}

Data aggregation

Description

Aggregates the expression result using the specified aggregation method in the current Datashield session.

Usage

datashield.aggregate(conns, expr, async = TRUE, success = NULL, error = NULL)

Arguments

conns

DSConnection-class object or a list of DSConnection-classs.

expr

Expression to evaluate.

async

Whether the result of the call should be retrieved asynchronously. When TRUE (default) the calls are parallelized over the connections, when the connection supports that feature, with an extra overhead of requests.

success

Callback function that will be called each time an aggregation result is received from a connection. The expected function signature is the connection/study name and the result value. Default is NULL (no callback).

error

Callback function that will be called each time the aggregation request has failed. The expected function signature is the connection/study name and the error message. Default is NULL (no callback).

Value

The result of the aggregation

Examples

## Not run: 
# call aggregate function on server side asynchronously
# i.e. each study connection will process the request in parallel
result <- datashield.aggregate(conns, expr = quote(someFunction(D, 123)))

# call aggregate function on server side synchronously, i.e. each study 
# connection will be called, one after the other, in a blocking way 
result <- datashield.aggregate(conns, expr = quote(someFunction(D, 123)), async = FALSE)

# call aggregate functions that are defined in the provided named list. 
# Connections are filtered by the list names.
result <- datashield.aggregate(conns,
  list(server1=quote(someFunction(D, 123)), server2=quote(someFunction(G, 456))))

# call aggregate function with callback functions
result <- datashield.aggregate(conns, expr = quote(someFunction(D, 123)),
  success = function(server, res) {
    # do something with server's result value
  },
  error = function(server, error) {
    # do something with server's error message
  })

## End(Not run)