#-------------------------------------- HEADER --------------------------------------------#
#' @title Sum of Squares
#' @description Computes the sum of squares for a given study variable.
#' @details It is a wrapper for the server side function \code{\link{getSquaredSum}}.
#' @param x a character, the name of a study variable.
#' @param datasources a list of opal object(s) obtained after login in to opal servers;
#' these objects hold also the data assign to R, as \code{data frame}, from opal datasources.
#' @return return a numeric value.
#' @author Paula Raissa Costa e Silva
#' @section Dependencies:
#' \code{\link{getSquaredSum}}
#' @export
#' @examples
#' ds.sumOfSquares(x='D$birth_weight')
#'
ds.sumOfSquares <- function(x=NULL, datasources=NULL) {
if(is.null(x)){
stop("Please provide the name of the input vector", call. = FALSE)
}
# if no opal login details are provided look for 'opal' objects in the environment
if(is.null(datasources)){
datasources <- findLoginObjects()
}
xnames <- extract(x)
varname <- xnames$elements
obj2lookfor <- xnames$holders
if(is.na(obj2lookfor)){
defined <- isDefined(datasources, varname)
} else {
defined <- isDefined(datasources, obj2lookfor)
}
#number of studies
num.sources <- length(datasources)
result <- list()
for (i in 1:num.sources) {
cally <- call("getSquaredSum", x)
result <- opal::datashield.aggregate(datasources, cally)
}
total.sum <- 0
for(value in result) {
total.sum <- total.sum + value
}
return(total.sum)
}
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