extract: Fix extracting from sparse datagrams if key is missing. (#51)

* Comments in electrochem

* Allow newer dgbowl-schema

* Sparse extract test

* Return an empty dict.

setup.py

@@ -42,7 +42,7 @@
         "chemicals>=1.0.0",
         "rdkit-pypi>=2022",
         "yadg>=4.1",
-        "dgbowl-schemas==106",
+        "dgbowl-schemas>=106",
         "matplotlib>=3.5.0",
     ],
     extras_require={

src/dgpost/transform/electrochemistry.py

@@ -213,6 +213,7 @@ def charge(
     ----------
     time
         An array of timestamps at which the instantaneous current was measured.
+        Defaults to the :class:`pd.Index` of the :class:`pd.DataFrame`.
 
     I
         Values of the instantaneous current.
@@ -273,9 +274,10 @@ def average_current(
     ----------
     time
         An array of timestamps at which the instantaneous current was measured.
+        Defaults to the :class:`pd.Index` of the :class:`pd.DataFrame`.
 
-    I
-        Values of the instantaneous current.
+    Q
+        Values of the overall charge.
 
     t0
         An optional timestamp representing the time at which charge was zero. If not

src/dgpost/utils/extract.py

@@ -142,7 +142,7 @@ def _get_key_recurse(data, keylist):
                     for i in ret
                 ]
             ):
-                return _get_key_recurse([i[key] for i in data], ["*"])
+                return _get_key_recurse([i.get(key, {}) for i in data], ["*"])
             else:
                 return [None], [ret]
     else:

tests/test_extract.py

@@ -141,6 +141,17 @@ def test_valid_datagram(datadir):
             },
             "ref.ca.single.pkl",
         ),
+        (  # ts12 - sparse extract with arrow and implicit
+            "sparse.dg.json",
+            {
+                "at": {"step": "a"},
+                "columns": [
+                    {"key": "derived->xin->*", "as": "a"},
+                    {"key": "derived->xin", "as": "b"},
+                ],
+            },
+            "ref.sparse.xin.pkl",
+        ),
     ],
 )
 def test_extract_single(inpath, spec, outpath, datadir):