diff --git a/src/aces/expand_shards.py b/src/aces/expand_shards.py
index cf0e5cd..9638092 100755
--- a/src/aces/expand_shards.py
+++ b/src/aces/expand_shards.py
@@ -1,30 +1,67 @@
 #!/usr/bin/env python
 
+import glob
+import os
+import re
 import sys
 
 
 def expand_shards(*shards: str) -> str:
-    """This function expands a set of shard prefixes and number of shards into a list of all shards.
+    """This function expands a set of shard prefixes and number of shards into a list of all shards or expands
+    a directory into a list of all files within it.
 
     This can be useful with Hydra applications where you wish to expand a list of options for the sweeper to
     sweep over but can't use an OmegaConf resolver as those are evaluated after the sweep has been
     initialized.
 
     Args:
-        shards: A list of shard prefixes and number of shards to expand.
+        shards: A list of shard prefixes and number of shards to expand, or a directory to list all files.
 
-    Returns: A comma-separated list of all shards, expanded to the specified number.
+    Returns: A comma-separated list of all shards, expanded to the specified number, or all files in the
+        directory.
 
     Examples:
+        >>> import polars as pl
+        >>> import tempfile
+        >>> from pathlib import Path
+
         >>> expand_shards("train/4", "val/IID/1", "val/prospective/1")
         'train/0,train/1,train/2,train/3,val/IID/0,val/prospective/0'
+        >>> expand_shards("data/data_4", "data/test_4")
+        'data/data_0,data/data_1,data/data_2,data/data_3,data/test_0,data/test_1,data/test_2,data/test_3'
+
+        >>> parquet_data = pl.DataFrame({
+        ...     "patient_id": [1, 1, 1, 2, 3],
+        ...     "timestamp": ["1/1/1989 00:00", "1/1/1989 01:00", "1/1/1989 01:00", "1/1/1989 02:00", None],
+        ...     "code": ['admission', 'discharge', 'discharge', 'admission', "gender"],
+        ... }).with_columns(pl.col("timestamp").str.strptime(pl.Datetime, format="%m/%d/%Y %H:%M"))
+
+        >>> with tempfile.TemporaryDirectory() as tmpdirname:
+        ...     for i in range(4):
+        ...         with tempfile.NamedTemporaryFile(mode="w", suffix=".parquet") as f:
+        ...             data_path = Path(tmpdirname + f"/file_{i}")
+        ...             parquet_data.write_parquet(data_path)
+        ...     result = expand_shards(tmpdirname)
+        ...     ','.join(sorted(os.path.basename(f) for f in result.split(',')))
+        'file_0,file_1,file_2,file_3'
     """
 
     result = []
     for arg in shards:
-        prefix = arg[: arg.rfind("/")]
-        num = int(arg[arg.rfind("/") + 1 :])
-        result.extend(f"{prefix}/{i}" for i in range(num))
+        if os.path.isdir(arg):
+            # If the argument is a directory, list all files in the directory
+            files = glob.glob(os.path.join(arg, "*"))
+            result.extend(files)
+        else:
+            # Otherwise, treat it as a shard prefix and number of shards
+            match = re.match(r"(.+)([/_])(\d+)$", arg)
+            if match:
+                prefix = match.group(1)
+                delimiter = match.group(2)
+                num = int(match.group(3))
+                result.extend(f"{prefix}{delimiter}{i}" for i in range(num))
+            else:
+                raise ValueError(f"Invalid shard format: {arg}")
 
     return ",".join(result)