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ds.levels.R
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ds.levels.R
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#'
#' @title Levels attributes of a server-side factor
#' @description This function provides access to the level attribute of
#' a factor variable stored on the server-side.
#' This function is similar to R function \code{levels}.
#' @details
#' Server function called: \code{levelsDS}
#' @param x a character string specifying the name of a factor variable.
#' @param datasources a list of \code{\link{DSConnection-class}}
#' objects obtained after login. If the \code{datasources} argument is not specified
#' the default set of connections will be used: see \code{\link{datashield.connections_default}}.
#' @return \code{ds.levels} returns to the client-side the levels of a factor
#' class variable stored in the server-side.
#' @author DataSHIELD Development Team
#' @export
#' @examples
#' \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 levels of the PM_BMI_CATEGORICAL variable
#' ds.levels(x = 'D$PM_BMI_CATEGORICAL',
#' datasources = connections)#all servers are used
#' ds.levels(x = 'D$PM_BMI_CATEGORICAL',
#' datasources = connections[2])#only the second server is used (study2)
#'
#' # Example 2: Get the levels of the LAB_TSC variable
#' # This example should not work because LAB_TSC is a continuous variable
#' ds.levels(x = 'D$LAB_TSC',
#' datasources = connections)
#'
#' # clear the Datashield R sessions and logout
#' datashield.logout(connections)
#'
#' }
#'
ds.levels = function(x=NULL, datasources=NULL) {
# look for DS connections
if(is.null(datasources)){
datasources <- datashield.connections_find()
}
if(is.null(x)){
stop("Please provide the name of the input vector!", call.=FALSE)
}
# the input variable might be given as column table (i.e. D$x)
# or just as a vector not attached to a table (i.e. x)
# we have to make sure the function deals with each case
xnames <- extract(x)
varname <- xnames$elements
obj2lookfor <- xnames$holders
# check if the input object(s) is(are) defined in all the studies
if(is.na(obj2lookfor)){
defined <- isDefined(datasources, varname)
}else{
defined <- isDefined(datasources, obj2lookfor)
}
# call the internal function that checks the input object is of the same class in all studies.
typ <- checkClass(datasources, x)
# the input object must be a factor
if(!('factor' %in% typ)){
stop("The input object must be a factor.", call.=FALSE)
}
cally <- paste0("levelsDS(", x, ")")
levels_all <- DSI::datashield.aggregate(datasources, as.symbol(cally))
return(levels_all)
}