How to mark lines based on one column value but set the color based on another column?

First of all, I would like to thanks the Altair community for posting tutorials/questions online! I learned a lot from the previous posts. But I couldn’t figure out how to color the line series based on the value of another column. A simple example is let’s say I want to make a scatter plot of property1 and property2 from the multi-dimension data set df, and I would like to color the points based on “legend_value”, but also want to connect the points from same “obj” (plotted with different shapes). How can I make the lines has the same color as the scattered points in this plot?

Thanks in advance!!!

df = pd.DataFrame({'Obj':['a','a','a','a','b','b','b','c','c','c','d','d'],
                   'property1':[1,2,3,4,7,8,9,4,5,6,5,6],
                   'property2':[0.1,0.2,0.3,0.4,0.35,0.4,0.45,0.8,1,1.2,0.5,0.8],
                   'legend_value':[1,1,1,1,2,2,2,1,1,1,3,3]})
display(df)
scatter = alt.Chart(df).mark_point().encode(
    alt.X('property1:Q', scale=alt.Scale(zero=False)),
    alt.Y('property2:Q', scale=alt.Scale(zero=False)),
    shape=alt.Shape('Obj:N',legend=None),
    color=alt.Color('legend_value:Q',scale=alt.Scale(scheme='rainbow')),
    opacity=alt.value(0.8) 
)

scatter_objectline = alt.Chart(df).mark_line().encode(
    alt.X('property1:Q',scale=alt.Scale(zero=False)),
    alt.Y('property2:Q',scale=alt.Scale(zero=False)),
    color=alt.Color('Obj:N',legend=None),
    opacity=alt.value(0.2) 
)

scatter+scatter_objectline

[jakevdp]

Awesome! I’ll close this issue; feel free to reopen if you run into another problem with this.

[DeerWhale]

ohhh that makes sense and the output is perfect!! Thank you so much for your patience and the continued help!!