归一化平行坐标

A Parallel Coordinates 图表是一种图表，允许您通过为每个数据点绘制一条单独的线来可视化 individual data points。

这样的图表可以通过在Altair中首先将数据转换为合适的表示来创建。

此示例显示了一个修改过的平行坐标图，使用了Iris数据集，y轴显示的是经过最小-最大处理后的值，而不是原始值。这是VegaLite版本的简化Altair版本

Method syntax

import altair as alt
from vega_datasets import data
from altair import datum

source = data.iris()

alt.Chart(source).transform_window(
    index='count()'
).transform_fold(
    ['petalLength', 'petalWidth', 'sepalLength', 'sepalWidth']
).transform_joinaggregate(
     min='min(value)',
     max='max(value)',
     groupby=['key']
).transform_calculate(
    minmax_value=(datum.value-datum.min)/(datum.max-datum.min),
    mid=(datum.min+datum.max)/2
).mark_line().encode(
    x='key:N',
    y='minmax_value:Q',
    color='species:N',
    detail='index:N',
    opacity=alt.value(0.5)
).properties(width=500)

Attribute syntax

import altair as alt
from vega_datasets import data
from altair import datum

source = data.iris()

alt.Chart(source).transform_window(
    index='count()'
).transform_fold(
    ['petalLength', 'petalWidth', 'sepalLength', 'sepalWidth']
).transform_joinaggregate(
     min='min(value)',
     max='max(value)',
     groupby=['key']
).transform_calculate(
    minmax_value=(datum.value-datum.min)/(datum.max-datum.min),
    mid=(datum.min+datum.max)/2
).mark_line().encode(
    x='key:N',
    y='minmax_value:Q',
    color='species:N',
    detail='index:N',
    opacity=alt.value(0.5)
).properties(width=500)


# No channel encoding options are specified in this chart
# so the code is the same as for the method-based syntax.