通过组合列值在Altair中绘制网格堆积条形图

如何解决通过组合列值在Altair中绘制网格堆积条形图

我想像示例Trellis Stacked Bar Chart那样绘制网格堆积条形图图。

我有这个数据集：

pd.DataFrame({
    
    'storage': ['dev01','dev01','dev02','dev03'],'project': ['omega','alpha','beta','omega','alpha'],'read': [3,114,27,82],'write': [70,45,655,203],'read-write': [313,322,89,90,12]
    
})

  storage project  read  write  read-write
0   dev01   omega     3     70         313
1   dev01   alpha     0      0         322
2   dev01    beta     0      0          45
3   dev02   omega   114     45          89
4   dev02    beta    27    655          90
5   dev03   alpha    82    203          12

我不知道如何指定read，write，read-write列作为altair的颜色/值。

解决方法

您的数据为宽格式，必须转换为长格式才能在Altair编码中使用。有关更多信息，请参见Altair文档中的Long-Form vs. Wide-Form Data。

这可以通过使用pd.melt修改Pandas中的输入数据来解决，但是使用Altair的Fold Transform在图表规范中进行此重塑通常更方便。例如：

import pandas as pd
import altair as alt

df = pd.DataFrame({
    'storage': ['dev01','dev01','dev02','dev03'],'project': ['omega','alpha','beta','omega','alpha'],'read': [3,114,27,82],'write': [70,45,655,203],'read-write': [313,322,89,90,12]
})

alt.Chart(df).transform_fold(
    ['read','write','read-write'],as_=['mode','value']
).mark_bar().encode(
    x='value:Q',y='project:N',column='storage:N',color='mode:N'
).properties(
    width=200
)

,

您需要将所需的列melt插入新列：

# assuming your DataFrame is assigned to `df`

cols_to_melt = ['read','read-write']
cols_to_keep = df.columns.difference(cols_to_melt)

df = df.melt(cols_to_keep,cols_to_melt,'mode')

因此您将获得以下信息：

   project storage        mode  value
0    omega   dev01        read      3
1    alpha   dev01        read      0
2     beta   dev01        read      0
3    omega   dev02        read    114
4     beta   dev02        read     27
5    alpha   dev03        read     82
6    omega   dev01       write     70
7    alpha   dev01       write      0
8     beta   dev01       write      0
9    omega   dev02       write     45
10    beta   dev02       write    655
11   alpha   dev03       write    203
12   omega   dev01  read-write    313
13   alpha   dev01  read-write    322
14    beta   dev01  read-write     45
15   omega   dev02  read-write     89
16    beta   dev02  read-write     90
17   alpha   dev03  read-write     12

然后在替代代码段中，使用color='site'代替color='mode'。