Hierarchy Filter (first pull request)

nomenclature/codelist.py

@@ -17,6 +17,7 @@
 )
 
 
+
 here = Path(__file__).parent.absolute()
 
 
@@ -524,7 +525,7 @@ def from_directory(cls, name: str, path: Path, file_glob_pattern: str = "**/*"):
             with open(yaml_file, "r", encoding="utf-8") as stream:
                 _code_list = yaml.safe_load(stream)
 
-            # a "region" codelist assumes a top-level key to be used as attribute
+            # a "region" codelist assumes a top-level category to be used as attribute
             for top_level_cat in _code_list:
                 for top_key, _codes in top_level_cat.items():
                     for item in _codes:
@@ -542,3 +543,28 @@ def from_directory(cls, name: str, path: Path, file_glob_pattern: str = "**/*"):
             mapping[code.name] = code
 
         return cls(name=name, mapping=mapping)
+
+    def hierarchy_filter(self, hierarchy: str) -> "RegionCodeList":
+        """A filter that returns the components within a provided hierarchy.
+
+        Parameters
+        ----------
+        hierarchy : str
+            The name of the hierarchy whose components you are looking for.
+
+        Raises
+        ------
+        ValueError
+            If User inputs a typo or a hierarchy not compatible with the given model.
+
+        Returns
+        -------
+        RegionCodeList
+            Returns a list of the component regions of the inputted hierarchy.
+        """
+
+        mapping = {k: v for (k, v) in self.mapping.items() if v.hierarchy == hierarchy}
+        if mapping:
+            return RegionCodeList(name=f"{hierarchy}", mapping=mapping)
+        else:
+            raise ValueError(f"No hierarchy found for {hierarchy}.")