在Altair中向散点图添加R值(相关性) [英] Adding R-value (correlation) to scatter chart in Altair

问题描述

因此，我正在研究Cars数据集，并希望将R值添加到散点图中.因此，我可以使用此代码使用 transform_regression 来添加散点图，以添加一个很棒的回归线.

So I am playing around with the Cars dataset and am looking to add the R-value to a scatter chart. So I can use this code to produce a scatter chart using transform_regression to add a regression line which is great.

from vega_datasets import data
import altair as alt
import pandas as pd
import numpy as np

cars = data.cars()
chart = alt.Chart(cars).mark_circle().encode(
        alt.X('Miles_per_Gallon', scale=alt.Scale(domain=(5,50))),
        y='Weight_in_lbs'
)

chart + chart.transform_regression('Miles_per_Gallon','Weight_in_lbs').mark_line()

这是图表

然后我正在寻找R值.因此可以在此代码中使用熊猫，因为我不确定如何使用Altair获取R值.

Then I am looking get the R-value. So can use pandas with this code as I am not sure how to get the R-value with Altair.

corl = cars[['Miles_per_Gallon','Weight_in_lbs']].corr().iloc[0,1]
corl

现在我想知道如何在图表上添加R值作为标签?

Now I was wondering how would I go about adding the R-value on the chart as a sort of label?

推荐答案

您可以通过添加文本层来做到这一点:

You can do this by adding a text layer:

text = alt.Chart({'values':[{}]}).mark_text(
    align="left", baseline="top"
).encode(
    x=alt.value(5),  # pixels from left
    y=alt.value(5),  # pixels from top
    text=alt.value(f"r: {corl:.3f}"),
)

chart + text + chart.transform_regression('Miles_per_Gallon','Weight_in_lbs').mark_line()

在以后的Altair版本中，将不再需要图表中的空白数据.

In future versions of Altair, the empty data in the chart will no longer be required.

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