diff --git a/molexpress/datasets/encoders.py b/molexpress/datasets/encoders.py
index d40d5b0..a3253a6 100644
--- a/molexpress/datasets/encoders.py
+++ b/molexpress/datasets/encoders.py
@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+from typing import Union
+
 import numpy as np
 
 from molexpress import types
@@ -23,27 +25,32 @@ def __call__(self, residues: list[types.Molecule | types.SMILES | types.InChI])
         for residue in residues:
             residue = chem_ops.get_molecule(residue)
             residue_graph = {
-                **self.node_encoder(residue), 
+                **self.node_encoder(residue),
                 **self.edge_encoder(residue)
             }
             residue_graphs.append(residue_graph)
             residue_sizes.append(residue.GetNumAtoms())
         disjoint_peptide_graph = self._merge_molecular_graphs(residue_graphs)
         disjoint_peptide_graph["residue_size"] = np.array(residue_sizes)
-        return disjoint_peptide_graph 
-    
+        disjoint_peptide_graph["peptide_size"] = np.array([len(residues)], dtype="int32")
+        return disjoint_peptide_graph
+
     @staticmethod
-    def _collate_fn(
-        data: list[tuple[types.MolecularGraph, np.ndarray]],
+    def collate_fn(
+        data: list[Union[types.MolecularGraph, tuple[types.MolecularGraph, np.ndarray]]],
     ) -> tuple[types.MolecularGraph, np.ndarray]:
-        """TODO: Not sure where to implement this collate function.
-                 Temporarily putting it here.
-
-        Procedure:
-            Merges list of graphs into a single disjoint graph.
         """
+        Merge list of graphs into a single disjoint graph.
 
-        disjoint_peptide_graphs, y = list(zip(*data))
+        Data can be a list of MolecularGraphs or a list of tuples where the first element is a
+        MolecularGraph and the second element is a label.
+
+        """
+        if isinstance(data[0], tuple):
+            disjoint_peptide_graphs, y = list(zip(*data))
+        else:
+            disjoint_peptide_graphs = data
+            y = None
 
         disjoint_peptide_batch_graph = PeptideGraphEncoder._merge_molecular_graphs(
             disjoint_peptide_graphs
@@ -54,7 +61,11 @@ def _collate_fn(
         disjoint_peptide_batch_graph["residue_size"] = np.concatenate([
             g["residue_size"] for g in disjoint_peptide_graphs
         ]).astype("int32")
-        return disjoint_peptide_batch_graph, np.stack(y)
+
+        if y is None:
+            return disjoint_peptide_batch_graph
+        else:
+            return disjoint_peptide_batch_graph, np.stack(y)
 
     @staticmethod
     def _merge_molecular_graphs(