Fix multi sourced belief charts (#228)

Multi-sourced beliefs now overlap rather than stack, and chart defaults are refactored to entire field definitions.


* Use full string representation for DataSource in JSON

* Update default chart to handle showing beliefs from multiple sources

* Refactor default field definition titles

* Move to setting defaults for entire field definitions, and add test

flexmeasures/data/models/charts/belief_charts.py

@@ -1,27 +1,28 @@
-from flexmeasures.data.models.charts.defaults import TIME_TITLE, TIME_TOOLTIP_TITLE
+from flexmeasures.data.models.charts.defaults import FIELD_DEFINITIONS
 
 
 def bar_chart(title: str, quantity: str = "unknown quantity", unit: str = "a.u."):
     if not unit:
         unit = "a.u."
+    event_value_field_definition = dict(
+        title=f"{quantity} ({unit})",
+        format=".3s",
+        stack=None,
+        **FIELD_DEFINITIONS["event_value"],
+    )
     return {
         "description": "A simple bar chart.",
         "title": title,
         "mark": "bar",
         "encoding": {
-            "x": {"field": "event_start", "type": "T", "title": TIME_TITLE},
-            "y": {
-                "field": "event_value",
-                "type": "quantitative",
-                "title": quantity + " (" + unit + ")",
-            },
+            "x": FIELD_DEFINITIONS["event_start"],
+            "y": event_value_field_definition,
+            "color": FIELD_DEFINITIONS["source"],
+            "opacity": {"value": 0.7},
             "tooltip": [
-                {"field": "full_date", "title": TIME_TOOLTIP_TITLE, "type": "nominal"},
-                {
-                    "field": "event_value",
-                    "title": quantity + " (" + unit + ")",
-                    "type": "quantitative",
-                },
+                FIELD_DEFINITIONS["full_date"],
+                event_value_field_definition,
+                FIELD_DEFINITIONS["source"],
             ],
         },
     }

flexmeasures/data/models/charts/defaults.py

@@ -9,9 +9,28 @@
 REDUCED_HEIGHT = REDUCED_WIDTH = 60
 SELECTOR_COLOR = "darkred"
 TIME_FORMAT = "%I:%M %p on %A %b %e, %Y"
-TIME_TOOLTIP_TITLE = "Time and date"
-TIME_TITLE = None
 TIME_SELECTION_TOOLTIP = "Click and drag to select a time window"
+FIELD_DEFINITIONS = {
+    "event_start": dict(
+        field="event_start",
+        type="temporal",
+        title=None,
+    ),
+    "event_value": dict(
+        field="event_value",
+        type="quantitative",
+    ),
+    "source": dict(
+        field="source",
+        type="ordinal",
+        title="Source",
+    ),
+    "full_date": dict(
+        field="full_date",
+        type="nominal",
+        title="Time and date",
+    ),
+}
 
 
 def apply_chart_defaults(fn):

flexmeasures/data/models/charts/test_chart_defaults.py

@@ -0,0 +1,9 @@
+import altair as alt
+
+from flexmeasures.data.models.charts.defaults import FIELD_DEFINITIONS
+
+
+def test_default_encodings():
+    """Check default encodings for valid vega-lite specifications."""
+    for field_name, field_definition in FIELD_DEFINITIONS.items():
+        assert alt.StringFieldDefWithCondition(**field_definition)

flexmeasures/data/models/time_series.py

@@ -97,7 +97,7 @@ def search_beliefs(
         )
         if as_json:
             df = bdf.reset_index()
-            df["source"] = df["source"].apply(lambda x: x.name)
+            df["source"] = df["source"].astype(str)
             return df.to_json(orient="records")
         return bdf