Flattens Server-Side Lists

Coerces an object of list class back to the class it was when it was coerced into a list.

ds.unList(x.name = NULL, newobj = NULL, datasources = NULL)

Arguments

x.name

a character string specifying the name of the input object to be unlisted.

newobj

a character string that provides the name for the output variable that is stored on the data servers. Default unlist.newobj.

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.unList returns to the server-side the unlist object. Also, two validity messages are returned to the client-side indicating whether the new object has been created in each data source and if so whether it is in a valid form.

Details

This function is similar to the native R function unlist.

When an object is coerced to a list, depending on the class of the original object some information may be lost. Thus, for example, when a data frame is coerced to list the information that underpins the structure of the data frame is lost and when it is subject to the function ds.unList it is returned to a simpler class than data frame e.g. numeric (basically a numeric vector containing all of the original data in all variables in the data frame but with no structure). If you wish to reconstruct the original data frame you, therefore, need to specify this structure again e.g. the column names, etc.

Server function called: unListDS

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") 
  
  #Create a list on the server-side
  
  ds.asList(x.name = "D", 
            newobj = "list.D",
            datasources = connections)
  
  #Flatten a server-side lists
  
  ds.unList(x.name = "list.D",
            newobj = "un.list.D",
           datasources = connections)
 
  # Clear the Datashield R sessions and logout                 
  datashield.logout(connections) 
  
} # }