Altair - 突出显示条形图中的单个元素

Question

我有这个 dagtaframe，talismen_players：

                        Team  TotalShots  TotalCreated  Goals  ...  WeightBetweenness  %ShotInv                     Player    Color
0                Aston Villa        55.0          68.0    7.0  ...               0.45      0.36              Jack Grealish  #770038
1            Manchester City        76.0          96.0    8.0  ...               0.44      0.32            Kevin De Bruyne  #97C1E7
2                    Watford        62.0          43.0    4.0  ...               0.37      0.34            Gerard Deulofeu  #FBEE23
3             Leicester City        60.0          67.0    6.0  ...               0.32      0.34             James Maddison  #0053A0
4               Norwich City        29.0          69.0    0.0  ...               0.31      0.32           Emiliano Buendia  #00A14E
5                    Chelsea        63.0          40.0    5.0  ...               0.28      0.23                Mason Mount  #034694
6          Tottenham Hotspur        64.0          30.0    9.0  ...               0.28      0.29              Son Heung-Min  #132257
7                    Everton        66.0          30.0   10.0  ...               0.22      0.26                Richarlison  #274488
8                    Arsenal        64.0          18.0   17.0  ...               0.21      0.27  Pierre-Emerick Aubameyang  #EF0107
9                Bournemouth        25.0          40.0    1.0  ...               0.21      0.23                Ryan Fraser  #D3151B
10            Crystal Palace        42.0          20.0    6.0  ...               0.20      0.24                Jordan Ayew  #C4122E
11                   Burnley        33.0          40.0    2.0  ...               0.20      0.27              Dwight McNeil  #630F33
12          Newcastle United        41.0          24.0    1.0  ...               0.20      0.24                  Joelinton  #231F20
13                 Liverpool        89.0          41.0   14.0  ...               0.18      0.31              Mohamed Salah  #CE1317
14  Brighton and Hove Albion        27.0          52.0    2.0  ...               0.16      0.23                Pascal Groß  #005DAA
15   Wolverhampton Wanderers        86.0          38.0   11.0  ...               0.16      0.38               Raul Jimenez  #FDB913
16          Sheffield United        31.0          35.0    5.0  ...               0.15      0.24                 John Fleck  #E52126
17           West Ham United        48.0          18.0    6.0  ...               0.15      0.25           Sebastien Haller  #7C2C3B
18               Southampton        64.0          21.0   15.0  ...               0.11      0.24                 Danny Ings  #ED1A3B
19         Manchester United        37.0          31.0    1.0  ...               0.10      0.17            Andreas Pereira  #E80909

我在altair 绘制的系列中挑出了一个元素，如下所示：

    target_team = 'Liverpool'
    # the following prints 'Mohamed Salah'
    target_player = talismen_players.loc[talismen_players['Team']==target_team, 'Player'].item()
    # all elements                
    talisman_chart = alt.Chart(talismen_players).mark_bar().encode(
            alt.Y('Player:N', title="", sort='-x'),
            alt.X('WeightBetweenness:Q', title="Interconectividade do craque com o resto do time"),
            alt.Color('Color', legend=None, scale=None),
            tooltip = [alt.Tooltip('Player:N'),
                       alt.Tooltip('Team:N'),
                       alt.Tooltip('TotalShots:Q'),
                       alt.Tooltip('%ShotInv:Q')],
        ).properties(
        width=800
        ).configure_axis(
        grid=False
        ).configure_view(
        strokeWidth=0
        )
_________

这绘制了所有元素，但我想突出显示其中一个：

这是使用行实现结果的代码：Multiline highlight

---

我已尝试使用此代码：

highlight = alt.selection(type='single', on='mouseover',
                      fields=['Player'], nearest=True)

base = alt.Chart(talismen_players).encode(
    alt.X('WeightBetweenness:Q'),
    alt.Y('Player:N', title=''),
    alt.Color('Color', legend=None, scale=None),
    tooltip = [alt.Tooltip('Player:N'),
                   alt.Tooltip('Team:N'),
                   alt.Tooltip('TotalShots:Q'),
                   alt.Tooltip('%ShotInv:Q')],
)

points = base.mark_circle().encode(
    opacity=alt.value(0)
).add_selection(
    highlight
).properties(
    width=700
)

lines = base.mark_bar().encode(
    size=alt.condition(~highlight, alt.value(18), alt.value(20))
)

但结果并不理想：

突出显示不起作用。

---

问题：

理想情况下，我希望target_player 栏默认突出显示。然后能够突出显示其他栏，鼠标悬停。

但是有target_player bar 静态突出显示就足够了。

高光不应改变条形颜色，而是具有焦点质量，而其他条形则失焦。

Answer 1

您可以使用初始化的选择以及用于突出显示的不透明度来执行此操作。例如：

import altair as alt
import pandas as pd

df = pd.DataFrame({
    'x': [1, 2, 3, 4],
    'y': ['A', 'B', 'C', 'D'],
    'color': ['W', 'X', 'Y', 'Z'],
})

hover = alt.selection_single(fields=['y'], on='mouseover', nearest=True, init={'y': 'C'})

alt.Chart(df).mark_bar().encode(
    x='x',
    y='y',
    color='color',
    opacity=alt.condition(hover, alt.value(1.0), alt.value(0.3))
).add_selection(hover)