Add capability to concat two FileContainers

filefinder/_filefinder.py

@@ -651,6 +651,37 @@ def search(self, **query):
         df = self._get_subset(**query)
         return type(self)(df)
 
+    def concat(self, other):
+        """concatenate two FileContainers
+
+        Parameters
+        ----------
+        other : FileContainer
+            The other FileContainer to concatenate.
+
+        Returns
+        -------
+        FileContainer
+            The concatenated FileContainer.
+
+        Raises
+        ------
+        ValueError
+            If the other object is not a FileContainer.
+        ValueError
+            If the two FileContainers do not have the same keys.
+        """
+
+        if not isinstance(other, FileContainer):
+            raise ValueError("Can only concatenate two FileContainers.")
+
+        if self.df.columns is not other.df.columns:
+            raise ValueError("FileContainers must have the same keys.")
+
+        ret = copy.copy(self)
+        ret.df = pd.concat([self.df, other.df])
+        return ret
+
     def _get_subset(self, **query):
         if not query:
             return pd.DataFrame(

filefinder/tests/test_filecontainer.py

@@ -140,6 +140,22 @@ def test_filecontainer_search(example_df, example_fc):
     pd.testing.assert_frame_equal(result.df, expected)
 
 
+def test_filecontainer_concat(example_fc):
+
+    with pytest.raises(ValueError, match="Can only concatenate two FileContainers."):
+        example_fc.concat("not a FileContainer")
+
+    with pytest.raises(ValueError, match="FileContainers must have the same keys"):
+        different_keys_fc = FileContainer(example_fc.df.loc[:, ["model", "scen"]])
+        example_fc.concat(different_keys_fc)
+
+    result = example_fc.concat(example_fc)
+    expected = pd.concat([example_fc.df, example_fc.df])
+
+    pd.testing.assert_frame_equal(result.df, expected)
+    assert result.__len__() == 10
+
+
 def test_fc_combine_by_key_deprecated(example_fc):
 
     with pytest.warns(FutureWarning, match="`combine_by_key` has been deprecated"):