fix: DH-19036: Fix failing subplot creation (#1176)

Originally failing was the following:

```
import deephaven.plot.express as dx
tips = dx.data.tips() # import a ticking version of the Tips dataset

# create 4 plots from within make_subplots
tipping_plots = dx.make_subplots(
    dx.scatter(tips, x="TotalBill", y="Tip", by="Sex",
        title="Tip amount by total bill"),
     dx.scatter(tips, x="TotalBill", y="Tip", by="Sex",
        title="Tip amount by total bill"),
    rows=2, cols=1, shared_xaxes=True, shared_yaxes=False
)
```

Added docs for shared axes as well

---------

Co-authored-by: margaretkennedy <82049573+margaretkennedy@users.noreply.github.com>

Author: jnumainville

plugins/plotly-express/docs/sub-plots.md

@@ -36,8 +36,110 @@ tipping_plots = dx.make_subplots(
 
 ![Sub Plot Basic Example](./_assets/sub_plot.png)
 
-## API Reference
+### Share Axes
+
+Share axes between plots with the `shared_xaxes` and `shared_yaxes` parameters.
+
+#### Share All Axes
+
+When `shared_xaxes` or `shared_yaxes` is set to `"all"`, all axes of the same type are shared.
+When one axis is adjusted, all axes are adjusted to match.
+
+```python order=tipping_plots,lunch_tips,dinner_tips
+import deephaven.plot.express as dx
+tips = dx.data.tips() # import a ticking version of the Tips dataset
+
+# filter the tips dataset for separate lunch and dinner charts
+lunch_tips = tips.where("Time = `Lunch`")
+dinner_tips = tips.where("Time = `Dinner`")
+
+# create chart that shares all axes
+tipping_plots = dx.make_subplots(
+    dx.scatter(lunch_tips, x="TotalBill", y="Tip", labels={"Tip": "Lunch Tips"}),
+    dx.scatter(dinner_tips, x="TotalBill", y="Tip", labels={"Tip": "Dinner Tips"}),
+    rows=2, shared_yaxes="all", shared_xaxes="all"
+)
+```
+
+#### Share Y Axes
+
+When `shared_yaxis` is set to `True`, all y axes are shared along the same row.
+When one y-axis is adjusted, all axes along the same row are adjusted to match.
+
+```python order=tipping_plots,lunch_tips,dinner_tips
+import deephaven.plot.express as dx
+tips = dx.data.tips() # import a ticking version of the Tips dataset
+
+# filter the tips dataset for separate lunch and dinner charts
+lunch_tips = tips.where("Time = `Lunch`")
+dinner_tips = tips.where("Time = `Dinner`")
+
+# create chart that shares y axes along the row
+tipping_plots = dx.make_subplots(
+    dx.scatter(lunch_tips, x="TotalBill", y="Tip", labels={"Tip": "Lunch Tips"}),
+     dx.scatter(dinner_tips, x="TotalBill", y="Tip", labels={"Tip": "Dinner Tips"}),
+    cols=2, shared_yaxes=True
+)
+```
+
+To share the y axes along the same column, set `shared_yaxes` to `"columns"`.
+
+```python order=tipping_plots,lunch_tips,dinner_tips
+import deephaven.plot.express as dx
+tips = dx.data.tips() # import a ticking version of the Tips dataset
 
+# filter the tips dataset for separate lunch and dinner charts
+lunch_tips = tips.where("Time = `Lunch`")
+dinner_tips = tips.where("Time = `Dinner`")
+
+# create chart that shares y axes along the column
+tipping_plots = dx.make_subplots(
+    dx.scatter(lunch_tips, x="TotalBill", y="Tip", labels={"Tip": "Lunch Tips"}),
+     dx.scatter(dinner_tips, x="TotalBill", y="Tip", labels={"Tip": "Dinner Tips"}),
+    rows=2, shared_yaxes="columns"
+)
+```
+
+#### Share X Axes
+
+When `shared_xaxis` is set to `True`, all x axes are shared along the same column.
+When one x-axis is adjusted, all axes along the same column are adjusted to match.
+
+```python order=tipping_plots,lunch_tips,dinner_tips
+import deephaven.plot.express as dx
+tips = dx.data.tips() # import a ticking version of the Tips dataset
+
+# filter the tips dataset for separate lunch and dinner charts
+lunch_tips = tips.where("Time = `Lunch`")
+dinner_tips = tips.where("Time = `Dinner`")
+
+# create chart that shares x axes along the column
+tipping_plots = dx.make_subplots(
+    dx.scatter(lunch_tips, x="TotalBill", y="Tip", labels={"Tip": "Lunch Tips"}),
+     dx.scatter(dinner_tips, x="TotalBill", y="Tip", labels={"Tip": "Dinner Tips"}),
+    rows=2, shared_xaxes=True
+)
+```
+
+To share the x axes along the same column, set `shared_yaxes` to `"columns"`.
+
+```python order=tipping_plots,lunch_tips,dinner_tips
+import deephaven.plot.express as dx
+tips = dx.data.tips() # import a ticking version of the Tips dataset
+
+# filter the tips dataset for separate lunch and dinner charts
+lunch_tips = tips.where("Time = `Lunch`")
+dinner_tips = tips.where("Time = `Dinner`")
+
+# create chart that shares x axes along the row
+tipping_plots = dx.make_subplots(
+    dx.scatter(lunch_tips, x="TotalBill", y="Tip", labels={"Tip": "Lunch Tips"}),
+     dx.scatter(dinner_tips, x="TotalBill", y="Tip", labels={"Tip": "Dinner Tips"}),
+    cols=2, shared_xaxes="rows"
+)
+```
+
+## API Reference
 ```{eval-rst}
 .. dhautofunction:: deephaven.plot.express.make_subplots
 ```

plugins/plotly-express/src/deephaven/plot/express/plots/_layer.py

@@ -270,6 +270,9 @@ def match_axes(
             # this is the base axis to match to, so matches is not added
             return {}
         if axis_index is not None:
+            if axis_index not in matches_axes[match_axis_key]:
+                # this is the first axis to match to, so add it
+                matches_axes[match_axis_key][axis_index] = new_trace_axis
             return {"matches": matches_axes[match_axis_key][axis_index]}
 
     return {}

plugins/plotly-express/src/deephaven/plot/express/plots/subplots.py

@@ -357,9 +357,9 @@ def make_subplots(
         calculated from rows and number of figs provided if not passed
         but rows is.
         One of rows or cols should be provided if passing figs directly.
-      shared_xaxes: "rows", "cols"/True, "all" or None depending on what axes
+      shared_xaxes: "rows", "columns"/True, "all" or None depending on what axes
         should be shared
-      shared_yaxes: "rows"/True, "cols", "all" or None depending on what axes
+      shared_yaxes: "rows"/True, "columns", "all" or None depending on what axes
         should be shared
       grid: A grid (list of lists) of figures to draw. None can be
         provided in a grid entry