Fix igraph name scrambling when graph has no vertex names

Co-authored-by: frederikfabriciusbjerre <55752995+frederikfabriciusbjerre@users.noreply.github.com>

Author: Copilot

R/as_caugi.R

@@ -75,6 +75,7 @@ S7::method(
 
   n_edges <- igraph::ecount(x)
   directed <- igraph::is_directed(x)
+  has_names <- !is.null(igraph::V(x)$name)
   nm <- igraph::V(x)$name
   if (is.null(nm)) nm <- paste0("V", seq_len(igraph::vcount(x)))
 
@@ -93,11 +94,19 @@ S7::method(
     ))
   }
 
-  e <- igraph::ends(x, igraph::E(x), names = TRUE)
+  # Use names = FALSE when graph has no names to get numeric indices,
+  # then map to our generated names. This preserves vertex order.
+  e <- igraph::ends(x, igraph::E(x), names = has_names)
   glyph <- if (directed) "-->" else "---"
 
-  from <- e[, 1]
-  to <- e[, 2]
+  if (has_names) {
+    from <- e[, 1]
+    to <- e[, 2]
+  } else {
+    # Map numeric indices to our generated names
+    from <- nm[e[, 1]]
+    to <- nm[e[, 2]]
+  }
   edge <- rep_len(glyph, length.out = nrow(e))
 
   # collapse symmetrical edges

tests/testthat/test-as_caugi.R

@@ -236,6 +236,30 @@ test_that("igraph vertex order is preserved when converting to caugi", {
   expect_equal(V(cg)$name, paste0("V", 1:10))
 })
 
+test_that("igraph without names: vertex order is preserved (issue #XX)", {
+  skip_if_not_installed("igraph")
+
+  # Create igraph WITHOUT names - this is the exact issue scenario
+  # When no name is given to igraph, the order should not be scrambled
+  set.seed(1023)
+  ig <- igraph::sample_gnm(100, 500) |> igraph::as_directed(mode = "acyclic")
+  # Verify the graph has no names
+  expect_null(igraph::V(ig)$name)
+
+  # Convert to caugi - names should be generated in order V1, V2, ..., V100
+  cg <- as_caugi(ig, class = "DAG")
+
+  # The nodes should be in sequential order V1, V2, ..., V100
+  expected_names <- paste0("V", 1:100)
+  expect_equal(cg@nodes$name, expected_names)
+
+  # Also verify edges use the correct node names
+  edges_df <- as.data.frame(edges(cg))
+  # All from/to values should be valid names from expected_names
+  expect_true(all(edges_df$from %in% expected_names))
+  expect_true(all(edges_df$to %in% expected_names))
+})
+
 # ──────────────────────────────────────────────────────────────────────────────
 # ─────────────────────────── graphNEL conversion ──────────────────────────────
 # ──────────────────────────────────────────────────────────────────────────────