Why does setting hue in seaborn plot change the size of a point?

Question

The plot I am trying to make needs to achieve 3 things.

1. If a quiz is taken on the same day with the same score, that point needs to be bigger.
2. If two quiz scores overlap there needs to be some jitter so we can see all points.
3. Each quiz needs to have its own color

Here is how I am going about it.

 import seaborn as sns
 import pandas as pd
 data = {'Quiz': [1, 1, 2, 1, 2, 1],
         'Score': [7.5, 5.0, 10, 10, 10, 10],
         'Day': [2, 5, 5, 5, 11, 11],
         'Size': [115, 115, 115, 115, 115, 355]}

 df = pd.DataFrame.from_dict(data)

sns.lmplot(x = 'Day', y='Score', data = df, fit_reg=False, x_jitter = True, scatter_kws={'s': df.Size})
plt.show()

Setting the hue, which almost does everything I need, results in this.

 import seaborn as sns
 import pandas as pd
 data = {'Quiz': [1, 1, 2, 1, 2, 1],
         'Score': [7.5, 5.0, 10, 10, 10, 10],
         'Day': [2, 5, 5, 5, 11, 11],
         'Size': [115, 115, 115, 115, 115, 355]}

 df = pd.DataFrame.from_dict(data)

sns.lmplot(x = 'Day', y='Score', data = df, fit_reg=False, hue = 'Quiz', x_jitter = True, scatter_kws={'s': df.Size})
plt.show()

Is there a way I can have hue while keeping the size of my points?

Answer 1

It doesn't work because when you are using hue , seaborn does two separate scatterplots and therefore the size argument you are passing using scatter_kws= no longer aligns with the content of the dataframe.

You can recreate the same effect by hand however:

x_col = 'Day'
y_col = 'Score'
hue_col = 'Quiz'
size_col = 'Size'
jitter=0.2

fig, ax = plt.subplots()
for q,temp in df.groupby(hue_col):
    n = len(temp[x_col])
    x = temp[x_col]+np.random.normal(scale=0.2, size=(n,))
    ax.scatter(x,temp[y_col],s=temp[size_col], label=q)
ax.set_xlabel(x_col)
ax.set_ylabel(y_col)
ax.legend(title=hue_col)