BUG: groupby.hist legend should use group keys

Author: rhshadrach

pandas/plotting/_matplotlib/hist.py

@@ -292,6 +292,7 @@ def hist_series(
     yrot=None,
     figsize=None,
     bins=10,
+    legend=False,
     **kwds,
 ):
     import matplotlib.pyplot as plt
@@ -310,8 +311,11 @@ def hist_series(
         elif ax.get_figure() != fig:
             raise AssertionError("passed axis not bound to passed figure")
         values = self.dropna().values
-
+        if legend and "label" not in kwds:
+            kwds["label"] = self.name
         ax.hist(values, bins=bins, **kwds)
+        if legend:
+            ax.legend()
         ax.grid(grid)
         axes = np.array([ax])
 
@@ -360,6 +364,7 @@ def hist_frame(
     figsize=None,
     layout=None,
     bins=10,
+    legend=False,
     **kwds,
 ):
     if by is not None:
@@ -405,9 +410,14 @@ def hist_frame(
 
     for i, col in enumerate(com.try_sort(data.columns)):
         ax = _axes[i]
+        if legend and "label" not in kwds:
+            kwds["label"] = col
         ax.hist(data[col].dropna().values, bins=bins, **kwds)
         ax.set_title(col)
         ax.grid(grid)
+        if legend:
+            ax.legend()
+            kwds.pop("label")
 
     _set_ticks_props(
         axes, xlabelsize=xlabelsize, xrot=xrot, ylabelsize=ylabelsize, yrot=yrot