Fix order of edge or vertex attributes

When edge or vertex attributes are added via `add.attributes.to.network`, as of
igraph version 1.4.0, existing attributes are not re-added or re-ordered. That
is, if attributes `name` and `type` already exist and ones adds the new
attributes `kind` and `type`, then `kind` is added after `type` as `type`
already existed. However, this breaks the ordering of the attributes and leads
to failing tests, as the order of the attributes is also tested in some of our
tests. To fix this problem, remove and re-add an attribute that was already
present before. This way, we make sure that the new attributes are added in the
expected order. (The only exception is the `name` attribute: This attribute is
expected to be the first attribute, and it should not be removed and readded as
this could lead to serious problems.)

This addresses se-sic#236.

Signed-off-by: Thomas Bock <bockthom@cs.uni-saarland.de>

util-networks.R

@@ -1367,11 +1367,15 @@ add.attributes.to.network = function(network, type = c("vertex", "edge"), attrib
     ## get type
     type = match.arg(type, several.ok = FALSE)
 
-    ## get corresponding attribute function
+    ## get corresponding attribute functions
     if (type == "vertex") {
-        attribute.function = igraph::set.vertex.attribute # sprintf("igraph::set.%s.attribute", type)
+        attribute.set.function = igraph::set.vertex.attribute # sprintf("igraph::set.%s.attribute", type)
+        attribute.get.function = igraph::get.vertex.attribute # sprintf("igraph::get.%s.attribute", type)
+        attribute.remove.function = igraph::remove.vertex.attribute # sprintf("igraph::remove.%s.attribute", type)
     } else {
-        attribute.function = igraph::set.edge.attribute # sprintf("igraph::set.%s.attribute", type)
+        attribute.set.function = igraph::set.edge.attribute # sprintf("igraph::set.%s.attribute", type)
+        attribute.get.function = igraph::get.edge.attribute # sprintf("igraph::get.%s.attribute", type)
+        attribute.remove.function = igraph::remove.edge.attribute # sprintf("igraph::remove.%s.attribute", type)
     }
 
     ## iterate over all wanted attribute names and add the attribute with the wanted class
@@ -1385,6 +1389,16 @@ add.attributes.to.network = function(network, type = c("vertex", "edge"), attrib
         if (lubridate::is.POSIXct(default.value)) {
             attr(default.value, "tzone") = TIMEZONE
         }
+
+        ## check if the attribute is already present. If so, remove it and re-add it (to keep the intended order).
+        ## only exception from this: the name attribute is not removed and re-added, as this would lead to problems.
+        if (!is.null(attribute.get.function(network, attr.name)) && attr.name != "name") {
+            logging::logwarn("Attribute %s has already been present, but is re-added now.", attr.name)
+            present.value = attribute.get.function(network, attr.name)
+            network = attribute.remove.function(network, attr.name)
+            default.value = present.value
+        }
+
         ## add the new attribute to the network with the proper class
         network = attribute.set.function(network, attr.name, value = default.value)
     }