Calling scatterplot with size and hue raises TypeError

[ChristofKaufmann]

This small example

import seaborn as sns
df = sns.load_dataset('attention', index_col=0)
sns.scatterplot(df, x='subject', y='score', s=df['solutions']*20, hue='attention')

results in a TypeError.

Traceback

TypeError                                 Traceback (most recent call last)
File example.py:3
      1 import seaborn as sns
      2 df = sns.load_dataset('attention', index_col=0)
----> 3 sns.scatterplot(df, x='subject', y='score', s=df['solutions']*20, hue='attention')

File ~/.local/opt/mambaforge/envs/ml/lib/python3.10/site-packages/seaborn/relational.py:624, in scatterplot(data, x, y, hue, size, style, palette, hue_order, hue_norm, sizes, size_order, size_norm, markers, style_order, legend, ax, **kwargs)
    621 color = kwargs.pop("color", None)
    622 kwargs["color"] = _default_color(ax.scatter, hue, color, kwargs)
--> 624 p.plot(ax, kwargs)
    626 return ax

File ~/.local/opt/mambaforge/envs/ml/lib/python3.10/site-packages/seaborn/relational.py:458, in _ScatterPlotter.plot(self, ax, kws)
    456 if self.legend:
    457     attrs = {"hue": "color", "size": "s", "style": None}
--> 458     self.add_legend_data(ax, _scatter_legend_artist, kws, attrs)
    459     handles, _ = ax.get_legend_handles_labels()
    460     if handles:

File ~/.local/opt/mambaforge/envs/ml/lib/python3.10/site-packages/seaborn/_base.py:1270, in VectorPlotter.add_legend_data(self, ax, func, common_kws, attrs, semantic_kws)
   1268     if attr in kws:
   1269         level_kws[attr] = kws[attr]
-> 1270 artist = func(label=label, **{"color": ".2", **common_kws, **level_kws})
   1271 if _version_predates(mpl, "3.5.0"):
   1272     if isinstance(artist, mpl.lines.Line2D):

File ~/.local/opt/mambaforge/envs/ml/lib/python3.10/site-packages/seaborn/utils.py:927, in _scatter_legend_artist(**kws)
    924     else:
    925         line_kws["markeredgecolor"] = edgecolor
--> 927 return mpl.lines.Line2D([], [], **line_kws)

File ~/.local/opt/mambaforge/envs/ml/lib/python3.10/site-packages/matplotlib/lines.py:393, in Line2D.__init__(self, xdata, ydata, linewidth, linestyle, color, gapcolor, marker, markersize, markeredgewidth, markeredgecolor, markerfacecolor, markerfacecoloralt, fillstyle, antialiased, dash_capstyle, solid_capstyle, dash_joinstyle, solid_joinstyle, pickradius, drawstyle, markevery, **kwargs)
    391 self.set_markevery(markevery)
    392 self.set_antialiased(antialiased)
--> 393 self.set_markersize(markersize)
    395 self._markeredgecolor = None
    396 self._markeredgewidth = None

File ~/.local/opt/mambaforge/envs/ml/lib/python3.10/site-packages/matplotlib/lines.py:1265, in Line2D.set_markersize(self, sz)
   1256 def set_markersize(self, sz):
   1257     """
   1258     Set the marker size in points.
   1259 
   (...)
   1263          Marker size, in points.
   1264     """
-> 1265     sz = float(sz)
   1266     if self._markersize != sz:
   1267         self.stale = True

File ~/.local/opt/mambaforge/envs/ml/lib/python3.10/site-packages/pandas/core/series.py:248, in _coerce_method.<locals>.wrapper(self)
    240     warnings.warn(
    241         f"Calling {converter.__name__} on a single element Series is "
    242         "deprecated and will raise a TypeError in the future. "
   (...)
    245         stacklevel=find_stack_level(),
    246     )
    247     return converter(self.iloc[0])
--> 248 raise TypeError(f"cannot convert the series to {converter}")

TypeError: cannot convert the series to <class 'float'>

This applies to versions:

• 0.13.2
• 0.13.1
• 0.13.0

but not to 0.12.2. I did not test current git development version.

When calling scatterplot with hue a legend will be added. Together with s with different sizes this bug is triggered. The bug is not triggered, when...

• setting legend=False
• removing the hue argument (because no legend)
• removing the s argument
• setting the s argument to a scaler, like s=20

My interpretation is that the legend artist should receive a scaler, but gets an array. So maybe this issue has the same roots as #3575.

[mwaskom]

Why not use seaborn's size parameter here?

[ChristofKaufmann]

A colleague and I were so focused on the difference by the version, that we just didn't think of it. Thank you!

[mwaskom]

I do think it’s a real issue and know the cause (0.13.0 started propagating more user kwargs to the legend artists, but artists don’t have a s parameter). Just mentioning size= as in most cases I’d think that’s preferred (you don’t need to scale the units yourself and you get a legend).