Altair '4.1.0' 返回一个空图表

Question

I'm trying to add a symbol in my Altair chart so the user could know by color what each line represents in the chart, but when I plot it I receive an empty chart without the data I'm passing.

Meanwhile I was debugging the code and I suppose the problem is located on the line color = alt.Color...

base = alt.Chart(new_df, title="Mean Control Chart").properties(width=600,height=500)

domain = ['Mean','LSC','LM','LIC','1 x S(+)','2 x S(+)','1 x S(-)','2 x S(-)']
range_ = ['black','red','green','red','blue','blue','blue','blue']

# Linha da media
media_chart = base.mark_line(point=True).encode(
    alt.X('amostra',type='quantitative', title='Samples', scale=alt.Scale(domain=(x_range_min_1,x_range_max_1))),
    alt.Y('media', type='quantitative', title='Mean', scale=alt.Scale(domain=(y_range_min_1,y_range_max_1))),
    color = alt.Color('Symbol',type='nominal', scale=alt.Scale(domain=domain, range=range_))
)

Dataset

Answer 1

You cannot use "Symbol" as the chart color because it is not a column in your dataframe. You would need to reshape/melt the df first to create this column, eg with new_df.melt(id_vars=['amostra', 'media'], var_name='Symbol'] as per the pandas docs on reshaping .