enh: add interface to get corresponding file with given extension

niworkflows/utils/bids.py

@@ -488,3 +488,37 @@ def check_pipeline_version(cvers, data_desc):
     dvers = desc.get("PipelineDescription", {}).get("Version", "0+unknown")
     if Version(cvers).public != Version(dvers).public:
         return "Previous output generated by version {} found.".format(dvers)
+
+def corresponding_file(in_file, bids_dir, extension, bids_validate=True):
+    """
+    Returns the corresponding file with the given extension
+
+    Parameters
+    ----------
+    in_file : :obj:`str`
+        Filename
+    bids_dir : :obj:`str` or :obj:`bids.layout.BIDSLayout`
+        The BIDS directory
+    extension : :obj: `str`
+        An extension string
+    bids_validate : :obj:`bool`
+        Whether the `bids_dir` is validated upon initialization
+
+    Returns
+    -------
+    filename : :obj:`str`
+        The path to the corresponding file
+    """
+
+    if isinstance(bids_dir, BIDSLayout):
+        layout = bids_dir
+    else:
+        layout = BIDSLayout(str(bids_dir), validate=bids_validate)
+
+    entities = layout.parse_file_entities(in_file)
+    entities.pop("extension", None)
+    entities.pop("echo", None)
+    entities.pop("part", None)
+    corresponding_filename = layout.build_path(entities, extension=extension)
+
+    return corresponding_filename