facet_grid throws an error: ValueError: No objects to concatenate #734
Description
Minimum example to produce the bug using plotnine version 0.12.3
import numpy as np
import polars as pl
from plotnine import ggplot, geom_point, facet_grid, aes
tickers = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J']
keys = ['foo', 'bar', 'baz']
periods = [i for i in range(660)]
df = pl.DataFrame([(i, j, k) for i in tickers for j in keys for k in periods], ['ticker', 'key', 'period'])
.with_columns(value=pl.Series(np.random.rand(19800)))
(
ggplot(df, aes(x='period', y='value'))
+ geom_point()
+ facet_grid('ticker ~ key')
)
"""
########################################################
File .venv/lib/python3.8/site-packages/IPython/core/formatters.py:708, in PlainTextFormatter.call(self, obj)
701 stream = StringIO()
702 printer = pretty.RepresentationPrinter(stream, self.verbose,
703 self.max_width, self.newline,
704 max_seq_length=self.max_seq_length,
705 singleton_pprinters=self.singleton_printers,
706 type_pprinters=self.type_printers,
707 deferred_pprinters=self.deferred_printers)
--> 708 printer.pretty(obj)
709 printer.flush()
710 return stream.getvalue()
File .venv/lib/python3.8/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 .venv/lib/python3.8/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 .venv/lib/python3.8/site-packages/plotnine/ggplot.py:114, in ggplot.repr(self)
110 def repr(self) -> str:
111 """
112 Print/show the plot
113 """
--> 114 figure = self.draw(show=True)
116 dpi = figure.get_dpi()
117 W = int(figure.get_figwidth() * dpi)
File .venv/lib/python3.8/site-packages/plotnine/ggplot.py:224, in ggplot.draw(self, show)
222 self = deepcopy(self)
223 with plot_context(self, show=show):
--> 224 self._build()
226 # setup
227 figure, axs = self._create_figure()
File .venv/lib/python3.8/site-packages/plotnine/ggplot.py:328, in ggplot._build(self)
325 layout.map_position(layers)
327 # Apply and map statistics
--> 328 layers.compute_statistic(layout)
329 layers.map_statistic(self)
331 # Prepare data in geoms
332 # e.g. from y and width to ymin and ymax
File /.venv/lib/python3.8/site-packages/plotnine/layer.py:471, in Layers.compute_statistic(self, layout)
469 def compute_statistic(self, layout: Layout):
470 for l in self:
--> 471 l.compute_statistic(layout)
File .venv/lib/python3.8/site-packages/plotnine/layer.py:284, in layer.compute_statistic(self, layout)
282 data = self.stat.use_defaults(data)
283 data = self.stat.setup_data(data)
--> 284 data = self.stat.compute_layer(data, params, layout)
285 self.data = data
File .venv/lib/python3.8/site-packages/plotnine/stats/stat.py:306, in stat.compute_layer(cls, data, params, layout)
303 pscales = layout.get_scales(pdata["PANEL"].iat[0])
304 return cls.compute_panel(pdata, pscales, **params)
--> 306 return groupby_apply(data, "PANEL", fn)
File .venv/lib/python3.8/site-packages/plotnine/utils.py:597, in groupby_apply(df, cols, func, *args, **kwargs)
593 for _, d in df.groupby(cols, observed=True):
594 # function fn should be free to modify dataframe d, therefore
595 # do not mark d as a slice of df i.e no SettingWithCopyWarning
596 lst.append(func(d, *args, **kwargs))
--> 597 return pd.concat(lst, axis=axis, ignore_index=True)
File .venv/lib/python3.8/site-packages/pandas/core/reshape/concat.py:372, in concat(objs, axis, join, ignore_index, keys, levels, names, verify_integrity, sort, copy)
369 elif copy and using_copy_on_write():
370 copy = False
--> 372 op = _Concatenator(
373 objs,
374 axis=axis,
375 ignore_index=ignore_index,
376 join=join,
377 keys=keys,
378 levels=levels,
379 names=names,
380 verify_integrity=verify_integrity,
381 copy=copy,
382 sort=sort,
383 )
385 return op.get_result()
File .venv/lib/python3.8/site-packages/pandas/core/reshape/concat.py:429, in _Concatenator.init(self, objs, axis, join, keys, levels, names, ignore_index, verify_integrity, copy, sort)
426 objs = list(objs)
428 if len(objs) == 0:
--> 429 raise ValueError("No objects to concatenate")
431 if keys is None:
432 objs = list(com.not_none(*objs))
ValueError: No objects to concatenate
"""