From 4a7cf4cc40eaea503904e0b0bba1725217b7ca5c Mon Sep 17 00:00:00 2001
From: Varun Agrawal <varagrawal@gmail.com>
Date: Fri, 11 Apr 2025 15:19:24 -0400
Subject: [PATCH] update HybridNonlinearFactorGraph::restrict to ignore empty
 discrete factors

---
 gtsam/hybrid/HybridNonlinearFactorGraph.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/gtsam/hybrid/HybridNonlinearFactorGraph.cpp b/gtsam/hybrid/HybridNonlinearFactorGraph.cpp
index b42676aac..4f8cf45ee 100644
--- a/gtsam/hybrid/HybridNonlinearFactorGraph.cpp
+++ b/gtsam/hybrid/HybridNonlinearFactorGraph.cpp
@@ -237,12 +237,16 @@ HybridNonlinearFactorGraph HybridNonlinearFactorGraph::restrict(
     if (auto hf = dynamic_pointer_cast<HybridFactor>(f)) {
       result.push_back(hf->restrict(discreteValues));
     } else if (auto df = dynamic_pointer_cast<DiscreteFactor>(f)) {
-      result.push_back(df->restrict(discreteValues));
+      // In the case where all the values have been selected, we ignore the
+      // factor since it doesn't add any information
+      if (df->discreteKeys().size() > 0) {
+        result.push_back(df->restrict(discreteValues));
+      }
     } else {
       result.push_back(f);  // Everything else is just added as is
     }
   }
-  
+
   return result;
 }