ds.exp.R

#'
#' @title Computes the exponentials in the server-side
#' @description Computes the exponential values for a specified numeric vector. 
#' This function is similar to R function \code{exp}.
#' @details 
#' 
#' Server function called: \code{exp}. 
#' 
#' @param x a character string providing the name of a numerical vector.
#' @param newobj a character string that provides the name for the output variable
#' that is stored on the data servers. Default \code{exp.newobj}. 
#' @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.exp} returns a vector for each study of the exponential values for the numeric vector 
#' specified in the argument \code{x}. The created vectors are 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()
#'   
#'   # Log onto the remote Opal training servers
#'   connections <- DSI::datashield.login(logins = logindata, assign = TRUE, symbol = "D") 
#'   
#'   # compute exponential function of the 'PM_BMI_CONTINUOUS' variable
#'   ds.exp(x = "D$PM_BMI_CONTINUOUS",
#'          newobj = "exp.PM_BMI_CONTINUOUS",
#'          datasources = connections[1]) #only the first Opal server is used (study1)
#'
#'   # clear the Datashield R sessions and logout
#'   datashield.logout(connections) 
#'
#' }
#'
ds.exp = function(x=NULL, newobj=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 object!", 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)

  # call the internal function that checks the input object(s) is(are) of the same class in all studies.
  if(!('numeric' %in% typ) && !('integer' %in% typ)){
      stop(" Only objects of type 'numeric' and 'integer' are allowed.", call.=FALSE)
  }

  # create a name by default if user did not provide a name for the new variable
  if(is.null(newobj)){
    newobj <- "exp.newobj"
  }

  # call the server side function that does the job
  cally <- paste0('exp(', x, ')')
  DSI::datashield.assign(datasources, newobj, as.symbol(cally))


  # check that the new object has been created and display a message accordingly
  finalcheck <- isAssigned(datasources, newobj)

}