Scroll the runs table, pick a range, and choose what a comparison plots against

backend/fluksio/api/routes/runs.py

@@ -132,6 +132,9 @@ class MetricSeries(BaseModel):
 
 class SeriesAnswer(BaseModel):
     metric: str
+    #: What the x values are: "step", "time" (seconds since this run's first
+    #: reading), or the name of another metric this one was plotted against.
+    x: str = "step"
     lines: list[MetricSeries] = Field(default_factory=list)
 
 
@@ -356,13 +359,38 @@ def read_metrics(
     return rows
 
 
+def _points(session: Session, run_id: str, metric: str, x: str) -> list[list[float]]:
+    """One run's readings of ``metric``, against whichever x was asked for.
+
+    The step is the default because it is what every run has. Time answers
+    "which one got there sooner", and is measured from this run's own first
+    reading so that runs started hours apart still lie on top of each other.
+    Another metric answers "against what the loop was actually counting" — an
+    epoch, or samples seen — and is joined on the step the two share, which is
+    the only thing they have in common.
+    """
+    rows = _series(session, run_id, metric)
+    if x == "time":
+        if not rows:
+            return []
+        start = min(row.ts for row in rows)
+        return [[row.ts - start, row.value] for row in rows]
+    if x and x != "step":
+        against = {row.step: row.value for row in _series(session, run_id, x)}
+        return [[against[row.step], row.value] for row in rows if row.step in against]
+    return [[float(row.step), row.value] for row in rows]
+
+
 @router.get("/series/compare", response_model=SeriesAnswer)
-def compare_metric(session: SessionDep, ids: str, metric: str) -> Any:
+def compare_metric(session: SessionDep, ids: str, metric: str, x: str = "") -> Any:
     """One metric across several runs, as the chart widget's series shape.
 
     This is the comparison view: it answers in the same shape a flow answers a
     chart's query with, so putting three training curves beside each other is
     a widget binding rather than a screen of its own.
+
+    ``x`` names what to plot against — nothing or "step", "time", or another
+    metric of the same runs.
     """
     run_ids = [part for part in ids.split(",") if part]
     if not run_ids:
@@ -376,13 +404,10 @@ def compare_metric(session: SessionDep, ids: str, metric: str) -> Any:
         run = runs.get(run_id)
         if run is None:
             continue
-        rows = _series(session, run_id, metric)
         label = run_id
         if run.seed is not None:
             label = f"{run_id} (seed {run.seed})"
         lines.append(
-            MetricSeries(
-                label=label, points=[[float(row.step), row.value] for row in rows]
-            )
+            MetricSeries(label=label, points=_points(session, run_id, metric, x))
         )
-    return SeriesAnswer(metric=metric, lines=lines)
+    return SeriesAnswer(metric=metric, x=x or "step", lines=lines)