Bug when facetting, discrete position and multiple layers

[has2k1]

Multiple layers + discrete position aesthetic + facetting AND a facet which lacks a value in any one layer.

import pandas as pd
from plotnine import *

df1 = pd.DataFrame({
    'x': list("abc"),
    'y': [1, 2, 3],
    'g': list("AAA") # This layer would have no entry in the "B" facet
                     # triggering the bug
})

df2 = pd.DataFrame({
    'x': list("abc"),
    'y': [4, 5, 6],
    'g': list("AAB")
})

(ggplot(aes("x", "y"))
 + geom_point(df1)
 + geom_point(df2)
 + facet_wrap("g", scales="free_x")
)

Details

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
File ~/env/plotnine/scales/scale_xy.py:80, in scale_position_discrete.map(self, series, limits)
     79 try:
---> 80     seq = seq[idx]
     81 except IndexError:
     82     # Deal with missing data
     83     # - Insert NaN where there is no match

IndexError: arrays used as indices must be of integer (or boolean) type

During handling of the above exception, another exception occurred:

IndexError                                Traceback (most recent call last)
File ~/.pyenv/versions/3.10.4/envs/plotnine/lib/python3.10/site-packages/IPython/core/formatters.py:707, in PlainTextFormatter.__call__(self, obj)
    700 stream = StringIO()
    701 printer = pretty.RepresentationPrinter(stream, self.verbose,
    702     self.max_width, self.newline,
    703     max_seq_length=self.max_seq_length,
    704     singleton_pprinters=self.singleton_printers,
    705     type_pprinters=self.type_printers,
    706     deferred_pprinters=self.deferred_printers)
--> 707 printer.pretty(obj)
    708 printer.flush()
    709 return stream.getvalue()

File ~/.pyenv/versions/3.10.4/envs/plotnine/lib/python3.10/site-packages/IPython/lib/pretty.py:410, in RepresentationPrinter.pretty(self, obj)
    407                         return meth(obj, self, cycle)
    408                 if cls is not object \
    409                         and callable(cls.__dict__.get('__repr__')):
--> 410                     return _repr_pprint(obj, self, cycle)
    412     return _default_pprint(obj, self, cycle)
    413 finally:

File ~/.pyenv/versions/3.10.4/envs/plotnine/lib/python3.10/site-packages/IPython/lib/pretty.py:778, in _repr_pprint(obj, p, cycle)
    776 """A pprint that just redirects to the normal repr function."""
    777 # Find newlines and replace them with p.break_()
--> 778 output = repr(obj)
    779 lines = output.splitlines()
    780 with p.group():

File ~/env/plotnine/ggplot.py:101, in ggplot.__repr__(self)
     97 def __repr__(self):
     98     """
     99     Print/show the plot
    100     """
--> 101     self.__str__()
    102     return '<ggplot: (%d)>' % self.__hash__()

File ~/env/plotnine/ggplot.py:92, in ggplot.__str__(self)
     88 def __str__(self):
     89     """
     90     Print/show the plot
     91     """
---> 92     self.draw(show=True)
     94     # Return and empty string so that print(p) is "pretty"
     95     return ''

File ~/env/plotnine/ggplot.py:210, in ggplot.draw(self, return_ggplot, show)
    208 self = deepcopy(self)
    209 with plot_context(self, show=show):
--> 210     self._build()
    212     # setup
    213     figure, axs = self._create_figure()

File ~/env/plotnine/ggplot.py:307, in ggplot._build(self)
    304 # Map and train positions so that statistics have access
    305 # to ranges and all positions are numeric
    306 layout.train_position(layers, scales)
--> 307 layout.map_position(layers)
    309 # Apply and map statistics
    310 layers.compute_statistic(layout)

File ~/env/plotnine/facets/layout.py:108, in Layout.map_position(self, layers)
    105     x_vars = list(set(self.panel_scales_x[0].aesthetics) &
    106                   set(data.columns))
    107     SCALE_X = _layout['SCALE_X'].iloc[match_id].tolist()
--> 108     self.panel_scales_x.map(data, x_vars, SCALE_X)
    110 if self.panel_scales_y:
    111     y_vars = list(set(self.panel_scales_y[0].aesthetics) &
    112                   set(data.columns))

File ~/env/plotnine/scales/scales.py:165, in Scales.map(self, data, vars, idx)
    163 for i, sc in enumerate(self, start=1):
    164     bool_idx = (i == idx)
--> 165     results = sc.map(data.loc[bool_idx, col])
    166     if use_df:
    167         df.loc[bool_idx, col] = results

File ~/env/plotnine/scales/scale_xy.py:86, in scale_position_discrete.map(self, series, limits)
     84         seq = np.hstack((seq.astype(float), np.nan))
     85         idx = np.clip(idx, 0, len(seq)-1)
---> 86         seq = seq[idx]
     87     return seq
     88 return series

IndexError: arrays used as indices must be of integer (or boolean) type

Ref: https://stackoverflow.com/q/74369454/832573