Altair中的項目符號圖

Question

我試圖在Altair中重現這張Vega-lite圖表 ，但遇到一些問題。 這是我到目前為止的內容：

# data import and prep
import json
import altair as alt
import pandas as pd

df = pd.read_json("""[{"title":"Revenue","subtitle":"US$, in thousands","ranges":[150,225,300],"measures":[220,270],"markers":250},
{"title":"Profit","subtitle":"%","ranges":[20,25,30],"measures":[21,23],"markers":26},
{"title":"Order Size","subtitle":"US$, average","ranges":[350,500,600],"measures":[100,320],"markers":550},
{"title":"New Customers","subtitle":"count","ranges":[1400,2000,2500],"measures":[1000,1650],"markers":2100},
{"title":"Satisfaction","subtitle":"out of 5","ranges":[3.5,4.25,5],"measures":[3.2,4.7],"markers":4.4}]""")

df[['measure1','measure2']] = pd.DataFrame(df.measures.values.tolist(), index=df.index)

df[['low', 'medium', 'high']] = pd.DataFrame(df.ranges.values.tolist())

# chart
base = alt.Chart(df).encode(row = 'title:O')
m1 = base.mark_bar().encode(x='measure1:Q')
m2 = base.mark_tick().encode(x='measure2:Q')

到現在為止還挺好。 但是，當我嘗試對兩個圖表進行分層時：

m1 + m2

SchemaValidationError: Invalid specification

    altair.vegalite.v2.api.LayerChart->layer->items, validating 'anyOf'

    {'data': {'name': 'data-58353a9bcf31ee710e2a5cb2da21a143'}, 'mark': 'bar', 'encoding': {'row': {'type': 'nominal', 'field': 'title'}, 'x': {'type': 'quantitative', 'field': 'measure1'}}} is not valid under any of the given schemas

請注意，如果我在兩個圖層和最后一個方面都指定了y編碼，則此方法有效，但是這違背了具有多個切面的目的（所有Y軸標記都在所有切面中重復。如果我在基圖中未指定row編碼也不使用y編碼，只會繪制一個條形圖（最大的一個）。

我需要構面的原因是，鑒於數據的不同域，我可以指定獨立的x比例（請參見原始示例）。

謝謝你的幫助！

Answer 1

在Altair和vega-lite中，對兩個多面圖表進行分層都是無效的（通常，不能保證在分層時兩個多面圖表會對齊）。 如果您仔細觀察素食主義者圖表，您會發現它不是分層的多面圖，而是分層的圖。

在Altair中可以通過以下方式完成相同的操作：

import altair as alt
import pandas as pd

df = pd.DataFrame.from_records([
    {"title":"Revenue","subtitle":"US$, in thousands","ranges":[150,225,300],"measures":[220,270],"markers":[250]},
    {"title":"Profit","subtitle":"%","ranges":[20,25,30],"measures":[21,23],"markers":[26]},
    {"title":"Order Size","subtitle":"US$, average","ranges":[350,500,600],"measures":[100,320],"markers":[550]},
    {"title":"New Customers","subtitle":"count","ranges":[1400,2000,2500],"measures":[1000,1650],"markers":[2100]},
    {"title":"Satisfaction","subtitle":"out of 5","ranges":[3.5,4.25,5],"measures":[3.2,4.7],"markers":[4.4]}
])

alt.layer(
    alt.Chart().mark_bar(color='#eee').encode(alt.X("ranges[2]:Q", scale=alt.Scale(nice=False), title=None)),
    alt.Chart().mark_bar(color='#ddd').encode(x="ranges[1]:Q"),
    alt.Chart().mark_bar(color='#ccc').encode(x="ranges[0]:Q"),
    alt.Chart().mark_bar(color='lightsteelblue', size=10).encode(x='measures[1]:Q'),
    alt.Chart().mark_bar(color='steelblue', size=10).encode(x='measures[0]:Q'),
    alt.Chart().mark_tick(color='black').encode(x='markers[0]:Q'),
    data=df
).facet(
    row="title:O"
).resolve_scale(
    x='independent'
)

原始圖表中的某些樣式/配置選項丟失了，但這是一個粗略的主意。