correctly fall back to all numeric polars cols when y is not specified

hvplot/plotting/core.py

@@ -1882,13 +1882,21 @@ def _get_converter(self, x=None, y=None, kind=None, **kwds):
                     for v in params.values()
                     if isinstance(v, (str, list))
                 ]
+
                 columns = (
                     set(self._data.columns) & set(itertools.chain(*possible_columns))
                 ) or {self._data.columns[0]}
+                if y is None:
+                    # When y is not specified HoloViewsConverter finds all the numeric
+                    # columns and use them as y values (see _process_chart_y). We meed
+                    # to include these columns too.
+                    columns |= set(self._data.select(pl.col(pl.NUMERIC_DTYPES)).columns)
                 xs = x if is_list_like(x) else (x,)
                 ys = y if is_list_like(y) else (y,)
                 columns |= {*xs, *ys}
                 columns.discard(None)
+                # Reorder the columns as in the data.
+                columns = sorted(columns, key=lambda c: self._data.columns.index(c))
 
         if isinstance(self._data, pl.DataFrame):
             data = self._data.select(columns).to_pandas()

hvplot/tests/testplotting.py

@@ -67,4 +67,5 @@ def test_plot_supports_polars():
     pl = pytest.importorskip("polars")
     dfp = pl.DataFrame(pd._testing.makeDataFrame())
     out = plot(dfp, 'line')
-    assert isinstance(out, hv.Curve)
+    assert isinstance(out, hv.NdOverlay)
+    assert out.keys() == dfp.columns