[RLlib] Fix TorchMultiCategorical.to_deterministic to return a mult…

…i-dimensional tensor instead of a list. (ray-project#49098)

Signed-off-by: gexiaoxiao7 <1004083966@qq.com>

rllib/models/torch/torch_distributions.py

@@ -497,8 +497,17 @@ def from_logits(
 
         return TorchMultiCategorical(categoricals=categoricals)
 
-    def to_deterministic(self) -> "TorchMultiDistribution":
-        return TorchMultiDistribution([cat.to_deterministic() for cat in self._cats])
+    def to_deterministic(self) -> "TorchDeterministic":
+        if self._cats[0].probs is not None:
+            probs_or_logits = nn.utils.rnn.pad_sequence(
+                [cat.logits.t() for cat in self._cats], padding_value=-torch.inf
+            )
+        else:
+            probs_or_logits = nn.utils.rnn.pad_sequence(
+                [cat.logits.t() for cat in self._cats], padding_value=-torch.inf
+            )
+
+        return TorchDeterministic(loc=torch.argmax(probs_or_logits, dim=0))
 
 
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