fix: bug in acc_mutual_info slicing; add `target_delimiter` to uncond choices

lm_eval/api/task.py

@@ -1481,7 +1481,10 @@ class ConfigurableTask(Task):
                 # here mutual info refers to calculating
                 # log(P(choice|ctx) / P(choice)) = log(P(choice|ctx)) - log(P(choice))
                 # in other words normalizing by subtracting the unconditional logprob of each choice.
-                aux_arguments = [("", f"{choice}") for choice in choices]
+                # TODO: should these be strided? will have to modify the processing in process_results if so
+                aux_arguments = [
+                    ("", f"{target_delimiter}{choice}") for choice in choices
+                ]
 
                 arguments.extend(aux_arguments)
 
@@ -1580,11 +1583,12 @@ class ConfigurableTask(Task):
             ):
                 # then we are doing mutual info.
                 # this stores the "dryrun" / unconditional answer loglikelihoods
-                lls_unconditional = lls[1::2]
+                # as we extend the args list with unconditional ("", continuation) pairs
+                lls_unconditional = lls[len(choices) :]
                 if len(lls_unconditional) != len(choices):
                     raise ValueError
                 # and this stores our "regular" conditional loglikelihoods
-                lls = lls[::2]
+                lls = lls[: len(choices)]
 
             pred = np.argmax(lls)
             pred_norm = np.argmax(lls / completion_len)