Checks if a server-side vector is empty

this function is similar to R function is.na but instead of a vector of booleans it returns just one boolean to tell if all the elements are missing values.

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

Arguments

x

a character string specifying the name of the vector to check.

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.isNA returns a boolean. If it is TRUE the vector is empty (all values are NA), FALSE otherwise.

Details

In certain analyses such as GLM none of the variables should be missing at complete (i.e. missing value for each observation). Since in DataSHIELD it is not possible to see the data it is important to know whether or not a vector is empty to proceed accordingly.

Server function called: isNaDS

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 all the observation of the variable 'LAB_HDL' are missing (NA)
  ds.isNA(x = 'D$LAB_HDL',
          datasources = connections) #all servers are used
  ds.isNA(x = 'D$LAB_HDL',
          datasources = connections[1]) #only the first server is used (study1) 
 

  # clear the Datashield R sessions and logout
  datashield.logout(connections)

} # }