From 80a4cd1bfca60ce28667f000dce397435a5eaeda Mon Sep 17 00:00:00 2001
From: Frank Dellaert <dellaert@gmail.com>
Date: Sun, 29 Sep 2024 15:42:02 -0700
Subject: [PATCH] Only sample if not provided

---
 gtsam/discrete/DiscreteBayesNet.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/gtsam/discrete/DiscreteBayesNet.cpp b/gtsam/discrete/DiscreteBayesNet.cpp
index 1c5c81e45..56265b0a4 100644
--- a/gtsam/discrete/DiscreteBayesNet.cpp
+++ b/gtsam/discrete/DiscreteBayesNet.cpp
@@ -58,7 +58,12 @@ DiscreteValues DiscreteBayesNet::sample(DiscreteValues result) const {
   // sample each node in turn in topological sort order (parents first)
   for (auto it = std::make_reverse_iterator(end());
        it != std::make_reverse_iterator(begin()); ++it) {
-    (*it)->sampleInPlace(&result);
+    const DiscreteConditional::shared_ptr& conditional = *it;
+    // Sample the conditional only if value for j not already in result
+    const Key j = conditional->firstFrontalKey();
+    if (result.count(j) == 0) {
+      conditional->sampleInPlace(&result);
+    }
   }
   return result;
 }