Finalize 'metrics.centrality' function

Sort entries of resulting data frame and check whether the new default value
(that is computing the data.source directly from the network relations)
should be used or not.

See se-sic#195

util-networks.R

@@ -1610,3 +1610,24 @@ get.sample.network = function() {
 
     return(network)
 }
+
+
+## / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
+## Helper functions---------------------------------------------------------
+
+#' Calculate the data sources of a network based on its edge relations and compute all authors from these
+#'
+#' @param proj.data the \code{Proj.Data} object corresponding to the network
+#' @param network the network with the relations to be extracted
+#' @return a list of authors from the data sources of the relations in the network
+relations.to.authors = function(proj.data, network) {
+    ## get all relations in the network
+    data.sources = unique(E(net)$relation)
+
+    ## map them to data sources respectively using the defined translation constant
+    data.sources = apply(data.sources, 2, function(relation) {
+        return(RELATION.TO.DATASOURCE[relation])
+    })
+
+    return(get.authors.by.data.source(data.sources))
+}