Gets the length of an object in the server-side

This function gets the length of a vector or list that is stored on the server-side. This function is similar to the R function length.

ds.length(x = NULL, type = "both", checks = "FALSE", datasources = NULL)

Arguments

x

a character string specifying the name of a vector or list.

type

a character that represents the type of analysis to carry out. If type is set to 'combine', 'combined', 'combines' or 'c', a global length is returned if type is set to 'split', 'splits' or 's', the length is returned separately for each study. if type is set to 'both' or 'b', both sets of outputs are produced. Default 'both'.

checks

logical. If TRUE the model components are checked. Default FALSE to save time. It is suggested that checks should only be undertaken once the function call has failed.

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.length returns to the client-side the pooled length of a vector or a list, or the length of a vector or a list for each study separately.

Details

Server function called: lengthDS

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") 
  
  # Example 1: Get the total number of observations of the vector of
  # variable 'LAB_TSC' across all the studies
  ds.length(x = 'D$LAB_TSC', 
            type = 'combine',
            datasources = connections)

  # Example 2: Get the number of observations of the vector of variable
  # 'LAB_TSC' for each study separately
  ds.length(x = 'D$LAB_TSC',
            type = 'split',
            datasources = connections)

  # Example 3: Get the number of observations on each study and the total
  # number of observations across all the studies for the variable 'LAB_TSC'
  ds.length(x = 'D$LAB_TSC',
            type = 'both',
            datasources = connections)
  
  # clear the Datashield R sessions and logout
  datashield.logout(connections)
} # }