diff --git a/bayesflow/adapters/adapter.py b/bayesflow/adapters/adapter.py
index ebef412bf..9edbded92 100644
--- a/bayesflow/adapters/adapter.py
+++ b/bayesflow/adapters/adapter.py
@@ -233,11 +233,11 @@ def __len__(self):
 
     def apply(
         self,
+        include: str | Sequence[str] = None,
         *,
         forward: np.ufunc | str,
         inverse: np.ufunc | str = None,
         predicate: Predicate = None,
-        include: str | Sequence[str] = None,
         exclude: str | Sequence[str] = None,
         **kwargs,
     ):
@@ -388,6 +388,7 @@ def convert_dtype(
         exclude: str | Sequence[str] = None,
     ):
         """Append a :py:class:`~transforms.ConvertDType` transform to the adapter.
+        See also :py:meth:`~bayesflow.adapters.Adapter.map_dtype`.
 
         Parameters
         ----------
@@ -525,6 +526,24 @@ def log(self, keys: str | Sequence[str], *, p1: bool = False):
         self.transforms.append(transform)
         return self
 
+    def map_dtype(self, keys: str | Sequence[str], to_dtype: str):
+        """Append a :py:class:`~transforms.ConvertDType` transform to the adapter.
+        See also :py:meth:`~bayesflow.adapters.Adapter.convert_dtype`.
+
+        Parameters
+        ----------
+        keys : str or Sequence of str
+            The names of the variables to transform.
+        to_dtype : str
+            Target dtype
+        """
+        if isinstance(keys, str):
+            keys = [keys]
+
+        transform = MapTransform({key: ConvertDType(to_dtype) for key in keys})
+        self.transforms.append(transform)
+        return self
+
     def one_hot(self, keys: str | Sequence[str], num_classes: int):
         """Append a :py:class:`~transforms.OneHot` transform to the adapter.
 
@@ -590,9 +609,9 @@ def sqrt(self, keys: str | Sequence[str]):
 
     def standardize(
         self,
+        include: str | Sequence[str] = None,
         *,
         predicate: Predicate = None,
-        include: str | Sequence[str] = None,
         exclude: str | Sequence[str] = None,
         **kwargs,
     ):
@@ -621,9 +640,9 @@ def standardize(
 
     def to_array(
         self,
+        include: str | Sequence[str] = None,
         *,
         predicate: Predicate = None,
-        include: str | Sequence[str] = None,
         exclude: str | Sequence[str] = None,
         **kwargs,
     ):
diff --git a/bayesflow/adapters/transforms/filter_transform.py b/bayesflow/adapters/transforms/filter_transform.py
index 65f5750c8..706dd14d3 100644
--- a/bayesflow/adapters/transforms/filter_transform.py
+++ b/bayesflow/adapters/transforms/filter_transform.py
@@ -29,10 +29,10 @@ class FilterTransform(Transform):
 
     def __init__(
         self,
+        include: str | Sequence[str] = None,
         *,
         transform_constructor: Callable[..., ElementwiseTransform],
         predicate: Predicate = None,
-        include: str | Sequence[str] = None,
         exclude: str | Sequence[str] = None,
         **kwargs,
     ):
diff --git a/bayesflow/utils/empty.py b/bayesflow/utils/empty.py
new file mode 100644
index 000000000..14331dc37
--- /dev/null
+++ b/bayesflow/utils/empty.py
@@ -0,0 +1,13 @@
+class empty:
+    """
+    Placeholder value for arguments left empty
+
+    Usage:
+
+    def f(x=empty):
+        if x is empty:
+            # we know the user did not pass x
+        if x is None:
+            # the user could have passed None explicitly
+
+    """