Further improve construction of edgeless networks

When constructing a network in 'construct.network.from.edge.list', several corner cases need to be handled. When there are no edges available, an empty edge list can be created using 'create.empty.edge.list'. This way, reliably, the function 'igraph::graph.data.frame' can be used to construct a network. This further improves the patch 0d7c222, which tackles se-sic#150. Tests for creating edgeless networks are added to the file 'tests/test-networks.R'. This likely prevents regressions in the future. Additionally, use the function 'create.empty.edge.list' in one further place where possible. Signed-off-by: Claus Hunsen <[email protected]>
fehnkera · Sep 23, 2020 · 5df8938 · 5df8938
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diff --git a/tests/test-networks.R b/tests/test-networks.R
@@ -93,3 +93,57 @@ test_that("Merge networks", {
 
 })
 
+
+## / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /
+## Construction of edgeless networks ---------------------------------------
+
+test_that("Construction of edgeless networks", {
+
+    ## create data structures and network configuration as a basis
+    edge.list = data.frame(from = c("D1", "D2"), to   = c("D2", "D1"))
+    edge.list.as.sequence = as.vector(as.matrix(edge.list))
+    vertices = data.frame(name = c("D1", "D2"))
+    vertices.as.sequence = vertices[["name"]]
+    directed = FALSE # directedness does not matter for this test, but should be consistent
+    net.conf = NetworkConf$new()
+
+    ## construct edgeless network
+    net.edgeless = igraph::graph.empty(n = 0, directed = directed) +
+        igraph::vertices(vertices.as.sequence) +
+        igraph::edges(NULL, weight = 1)
+
+    ##
+    ## normal network
+    ##
+
+    net.constructed = construct.network.from.edge.list(vertices, edge.list, net.conf)
+    net.expected = igraph::graph.empty(n = 0, directed = directed) +
+        igraph::vertices(vertices.as.sequence) +
+        igraph::edges(edge.list.as.sequence, weight = 1)
+
+    ## check equality
+    expect_true(igraph::identical_graphs(net.constructed, net.expected), label = "normal network construction")
+
+    ##
+    ## edgeless network: NULL
+    ##
+
+    net.constructed = construct.network.from.edge.list(vertices, NULL, net.conf)
+    expect_true(igraph::identical_graphs(net.constructed, net.edgeless), label = "edgeless network: NULL")
+
+    ##
+    ## edgeless network: create.empty.edge.list()
+    ##
+
+    net.constructed = construct.network.from.edge.list(vertices, create.empty.edge.list(), net.conf)
+    expect_true(igraph::identical_graphs(net.constructed, net.edgeless), label = "edgeless network: create.empty.edge.list()")
+
+    ##
+    ## edgeless network: empty data.frame
+    ##
+
+    net.constructed = construct.network.from.edge.list(vertices, data.frame(), net.conf)
+    expect_true(igraph::identical_graphs(net.constructed, net.edgeless), label = "edgeless network: empty data.frame")
+
+})
+
diff --git a/util-networks.R b/util-networks.R
@@ -1053,17 +1053,15 @@ construct.network.from.edge.list = function(vertices, edge.list, network.conf, d
         return(create.empty.network(directed = directed))
     }
 
-    ## if we have nodes to create, but no edges
+    ## if we have nodes to create, but no edges, create an empty edge list
     if (is.null(edge.list) || nrow(edge.list) == 0) {
-        ## create network with only the vertices
-        net = igraph::graph.empty(n = 0, directed = directed) + igraph::vertices(t(nodes.processed))
-    }
-    ## if we have nodes and edges
-    else {
-        ## construct network from edge list
-        net = igraph::graph.data.frame(edge.list, directed = directed, vertices = nodes.processed)
+        edge.list = create.empty.edge.list()
     }
 
+    ## construct network from edge list
+    net = igraph::graph.data.frame(edge.list, directed = directed, vertices = nodes.processed)
+
+    ## initialize edge weights
     net = igraph::set.edge.attribute(net, "weight", value = 1)
 
     ## transform multiple edges to edge weights
@@ -1100,7 +1098,7 @@ merge.network.data = function(vertex.data, edge.data) {
     edges = plyr::rbind.fill(edge.data.filtered)
     ## 3) correct empty results
     if (is.null(edges)) {
-        edges = data.frame(from = character(0), to = character(0))
+        edges = create.empty.edge.list()
     }
 
     logging::logdebug("merge.network.data: finished.")