PERF/CLN: Avoid ravel in plotting (#58973)

* Avoid ravel in plotting

* Use reshape instead of ravel

* Add type ignore

Author: mroeschke

pandas/plotting/_matplotlib/boxplot.py

@@ -311,8 +311,6 @@ def _grouped_plot_by_column(
         layout=layout,
     )
 
-    _axes = flatten_axes(axes)
-
     # GH 45465: move the "by" label based on "vert"
     xlabel, ylabel = kwargs.pop("xlabel", None), kwargs.pop("ylabel", None)
     if kwargs.get("vert", True):
@@ -322,8 +320,7 @@ def _grouped_plot_by_column(
 
     ax_values = []
 
-    for i, col in enumerate(columns):
-        ax = _axes[i]
+    for ax, col in zip(flatten_axes(axes), columns):
         gp_col = grouped[col]
         keys, values = zip(*gp_col)
         re_plotf = plotf(keys, values, ax, xlabel=xlabel, ylabel=ylabel, **kwargs)
@@ -531,10 +528,8 @@ def boxplot_frame_groupby(
             figsize=figsize,
             layout=layout,
         )
-        axes = flatten_axes(axes)
-
         data = {}
-        for (key, group), ax in zip(grouped, axes):
+        for (key, group), ax in zip(grouped, flatten_axes(axes)):
             d = group.boxplot(
                 ax=ax, column=column, fontsize=fontsize, rot=rot, grid=grid, **kwds
             )

pandas/plotting/_matplotlib/core.py

@@ -586,7 +586,7 @@ def _axes_and_fig(self) -> tuple[Sequence[Axes], Figure]:
                 fig.set_size_inches(self.figsize)
             axes = self.ax
 
-        axes = flatten_axes(axes)
+        axes = np.fromiter(flatten_axes(axes), dtype=object)
 
         if self.logx is True or self.loglog is True:
             [a.set_xscale("log") for a in axes]

pandas/plotting/_matplotlib/hist.py

@@ -95,11 +95,12 @@ def _adjust_bins(self, bins: int | np.ndarray | list[np.ndarray]):
     def _calculate_bins(self, data: Series | DataFrame, bins) -> np.ndarray:
         """Calculate bins given data"""
         nd_values = data.infer_objects()._get_numeric_data()
-        values = np.ravel(nd_values)
+        values = nd_values.values
+        if nd_values.ndim == 2:
+            values = values.reshape(-1)
         values = values[~isna(values)]
 
-        hist, bins = np.histogram(values, bins=bins, range=self._bin_range)
-        return bins
+        return np.histogram_bin_edges(values, bins=bins, range=self._bin_range)
 
     # error: Signature of "_plot" incompatible with supertype "LinePlot"
     @classmethod
@@ -322,10 +323,7 @@ def _grouped_plot(
         naxes=naxes, figsize=figsize, sharex=sharex, sharey=sharey, ax=ax, layout=layout
     )
 
-    _axes = flatten_axes(axes)
-
-    for i, (key, group) in enumerate(grouped):
-        ax = _axes[i]
+    for ax, (key, group) in zip(flatten_axes(axes), grouped):
         if numeric_only and isinstance(group, ABCDataFrame):
             group = group._get_numeric_data()
         plotf(group, ax, **kwargs)
@@ -557,12 +555,9 @@ def hist_frame(
         figsize=figsize,
         layout=layout,
     )
-    _axes = flatten_axes(axes)
-
     can_set_label = "label" not in kwds
 
-    for i, col in enumerate(data.columns):
-        ax = _axes[i]
+    for ax, col in zip(flatten_axes(axes), data.columns):
         if legend and can_set_label:
             kwds["label"] = col
         ax.hist(data[col].dropna().values, bins=bins, **kwds)

pandas/plotting/_matplotlib/tools.py

@@ -18,7 +18,10 @@
 )
 
 if TYPE_CHECKING:
-    from collections.abc import Iterable
+    from collections.abc import (
+        Generator,
+        Iterable,
+    )
 
     from matplotlib.axes import Axes
     from matplotlib.axis import Axis
@@ -231,7 +234,7 @@ def create_subplots(
     else:
         if is_list_like(ax):
             if squeeze:
-                ax = flatten_axes(ax)
+                ax = np.fromiter(flatten_axes(ax), dtype=object)
             if layout is not None:
                 warnings.warn(
                     "When passing multiple axes, layout keyword is ignored.",
@@ -260,7 +263,7 @@ def create_subplots(
             if squeeze:
                 return fig, ax
             else:
-                return fig, flatten_axes(ax)
+                return fig, np.fromiter(flatten_axes(ax), dtype=object)
         else:
             warnings.warn(
                 "To output multiple subplots, the figure containing "
@@ -439,12 +442,13 @@ def handle_shared_axes(
                     _remove_labels_from_axis(ax.yaxis)
 
 
-def flatten_axes(axes: Axes | Iterable[Axes]) -> np.ndarray:
+def flatten_axes(axes: Axes | Iterable[Axes]) -> Generator[Axes, None, None]:
     if not is_list_like(axes):
-        return np.array([axes])
+        yield axes  # type: ignore[misc]
     elif isinstance(axes, (np.ndarray, ABCIndex)):
-        return np.asarray(axes).ravel()
-    return np.array(axes)
+        yield from np.asarray(axes).reshape(-1)
+    else:
+        yield from axes  # type: ignore[misc]
 
 
 def set_ticks_props(
@@ -456,13 +460,13 @@ def set_ticks_props(
 ):
     for ax in flatten_axes(axes):
         if xlabelsize is not None:
-            mpl.artist.setp(ax.get_xticklabels(), fontsize=xlabelsize)
+            mpl.artist.setp(ax.get_xticklabels(), fontsize=xlabelsize)  # type: ignore[arg-type]
         if xrot is not None:
-            mpl.artist.setp(ax.get_xticklabels(), rotation=xrot)
+            mpl.artist.setp(ax.get_xticklabels(), rotation=xrot)  # type: ignore[arg-type]
         if ylabelsize is not None:
-            mpl.artist.setp(ax.get_yticklabels(), fontsize=ylabelsize)
+            mpl.artist.setp(ax.get_yticklabels(), fontsize=ylabelsize)  # type: ignore[arg-type]
         if yrot is not None:
-            mpl.artist.setp(ax.get_yticklabels(), rotation=yrot)
+            mpl.artist.setp(ax.get_yticklabels(), rotation=yrot)  # type: ignore[arg-type]
     return axes