Checks if an object is defined on the server-side

Looks if an R object of the given name is defined on the server-side. This function is similar to the R function exists.

ds.exists(x = NULL, datasources = NULL)

Arguments

x

a character string providing the name of the object to look for.

datasources

a list of DSConnection-class objects obtained after login. If the datasources argument is not specified the default set of connections will be used: see datashield.connections_default.

Value

ds.exists returns a logical object. TRUE if the object is on the server-side and FALSE otherwise.

Details

In DataSHIELD it is not possible to see the data on the servers of the collaborating studies. It is only possible to get summaries of objects stored on the server-side. It is however important to know if an object is defined (i.e. exists) on the server-side. This function checks if an object does exist on the server-side.

Server function called: exists

See also

ds.class to check the type of an object.

ds.length to check the length of an object.

ds.dim to check the dimension of an object.

Author

DataSHIELD Development Team

Examples

if (FALSE) { # \dontrun{

  ## Version 6, for version 5 see the Wiki
  
  # connecting to the Opal servers

  require('DSI')
  require('DSOpal')
  require('dsBaseClient')

  builder <- DSI::newDSLoginBuilder()
  builder$append(server = "study1", 
                 url = "http://192.168.56.100:8080/", 
                 user = "administrator", password = "datashield_test&", 
                 table = "CNSIM.CNSIM1", driver = "OpalDriver")
  builder$append(server = "study2", 
                 url = "http://192.168.56.100:8080/", 
                 user = "administrator", password = "datashield_test&", 
                 table = "CNSIM.CNSIM2", driver = "OpalDriver")
  builder$append(server = "study3",
                 url = "http://192.168.56.100:8080/", 
                 user = "administrator", password = "datashield_test&", 
                 table = "CNSIM.CNSIM3", driver = "OpalDriver")
  logindata <- builder$build()
  
  connections <- DSI::datashield.login(logins = logindata, assign = TRUE, symbol = "D") 
  
  # Check if the object exist in the server-side
  ds.exists(x = "D", 
            datasources = connections) #All opal servers are used
  ds.exists(x = "D", 
            datasources = connections[1]) #Only the first Opal server is used (study1)
            
  # clear the Datashield R sessions and logout
  datashield.logout(connections)

} # }