how to grey out other lines using Mouse hover?

Question

I'm trying to grey out other lines when i hover over one of them so far i have this:

from sklearn import datasets
data_wine = datasets.load_wine (as_frame = True).frame
new_data = data_wine.drop (['proline', 'magnesium'], axis = 1)
new_data = new_data.reset_index().melt(id_vars = ['index', 'target'])
hover = alt.selection(
   type="single", on="mouseover", fields=["variable"], nearest=True
)

lineplot = alt.Chart(new_data).mark_line().encode(
   alt.X("variable:N"),
   alt.Y("value:Q"),
   alt.Color ('target:N'),
   alt.Detail ('index:N'),
).properties(width = 1000)

# nearest point
point = lineplot.mark_circle().encode(
   opacity=alt.value(0)
).add_selection(hover)
# highlight
singleline = lineplot.mark_line().encode(
   size=alt.condition(~hover, alt.value(0.5), alt.value(3))
)


point+singleline

it looks like this and while hovering the mouse the size changes and i couldn't replace size with Color:

how can i achieve this?

Answer 1

new_data = data_wine.drop (['proline', 'magnesium'], axis = 1)
new_data = new_data.reset_index().melt(id_vars = ['index', 'target'])

highlight = alt.selection(type='single', on='mouseover', fields=['target'], nearest=False, bind='legend')

selection = alt.selection_multi(fields=['target'], bind='legend', on='mouseover')

lineplot=alt.Chart(new_data).mark_line().encode(
   alt.X("variable:N"),
   alt.Y("value:Q"),
   alt.Color ('target:N'),
   alt.Detail ('index:N'),
).properties(width = 1000)


# nearest point
point = lineplot.mark_circle().encode(
    opacity=alt.value(0)
).add_selection(highlight)
#highlight
singleline = lineplot.mark_line().encode(
   opacity=alt.condition(selection, alt.value(0.7), alt.value(0.03))
   #size=alt.condition(~highlight, alt.value(1), alt.value(3))
).add_selection(selection)


point + singleline