将图例添加到Altair的分层图表中 [英] Adding legend to layerd chart in altair

问题描述

请考虑以下示例:

 导入altair为alt从vega_datasets导入数据df = data.seattle_weather()temp_max = alt.Chart(df).mark_line(color ='blue').encode(x ='yearmonth(date):T'，y ='max(temp_max)'，)temp_min = alt.Chart(df).mark_line(color='red').encode(x ='yearmonth(date):T'，y ='max(temp_min)'，)temp_max + temp_min 

在生成的图表中，我想添加一个图例，该图例显示蓝线显示最高温度，红线显示最低温度.最简单的方法是什么?

我看到了(例如，在该问题的解决方案中:

Consider the following example:

    import altair as alt
    from vega_datasets import data

    df = data.seattle_weather()

    temp_max = alt.Chart(df).mark_line(color='blue').encode(
        x='yearmonth(date):T',
        y='max(temp_max)',
    )

    temp_min = alt.Chart(df).mark_line(color='red').encode(
        x='yearmonth(date):T',
        y='max(temp_min)',
    )

    temp_max + temp_min

In the resulting chart, I would like to add a legend that shows, that the blue line shows the maximum temperature and the red line the minimum temperature. What would be the easiest way to achieve this?

I saw (e.g. in the solution to this question: Labelling Layered Charts in Altair (Python)) that altair only adds a legend if in the encoding, you set the color or size or so, usually with a categorical column, but that is not possible here because I'm plotting the whole column and the label should be the column name (which is now shown in the y-axis label).

解决方案

I would do a fold transform such that the variables could be encoded correctly.

import altair as alt
from vega_datasets import data

df = data.seattle_weather()

alt.Chart(df).mark_line().transform_fold(
    fold=['temp_max', 'temp_min'], 
    as_=['variable', 'value']
).encode(
    x='yearmonth(date):T',
    y='max(value):Q',
    color='variable:N'
)

这篇关于将图例添加到Altair的分层图表中的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！