问题
I try to create a Ridgeline plot in altair. Let's assume my dataframe consists of str and float columns:
a object
b float64
dtype: object
with values like
a b
0 25 2303.0
1 29 2676.0
2 18 2983.0
3 16 1489.0
4 21 3468.0
I used code from Altair gallery to create my chart: https://altair-viz.github.io/gallery/ridgeline_plot.html. My code with changed data and column names:
import pandas as np
import numpy as np
source = pd.DataFrame(columns=list('ab'))
source['a'] = np.random.randint(0,17,size=500)
source['a'] = source['a'].astype('str')
source['b'] = np.random.randint(1000,5000,size=500).astype('float')
import altair as alt
step = 20
overlap = 1
alt.Chart(source, height=step).transform_joinaggregate(
mean_temp='mean(b)', groupby=['a']
).transform_bin(
['bin_max', 'bin_min'], 'b'
).transform_aggregate(
value='count()', groupby=['a', 'b', 'bin_min', 'bin_max']
).transform_impute(
impute='value', groupby=['a', 'b'], key='bin_min', value=0
).mark_area(
interpolate='monotone',
fillOpacity=0.8,
stroke='lightgray',
strokeWidth=0.5
).encode(
alt.X('bin_min:Q', bin='binned', title=''),
alt.Y(
'value:Q',
scale=alt.Scale(range=[step, -step * overlap]),
axis=None
),
alt.Fill(
'b:Q',
legend=None,
)
).facet(
row=alt.Row(
'a:T',
title=None,
header=alt.Header(labelAngle=0, labelAlign='right', format='%B')
)
).properties(
title='',
bounds='flush'
).configure_facet(
spacing=0
).configure_view(
stroke=None
).configure_title(
anchor='end'
)
When I use row=alt.Row('a:T'...)
it thinks my data is temporal month, but works fine:
But when I change type there to nominal 'a:N'
, result is empty. How to fix it?
回答1:
For chart rendering errors like this, often there are clues in the browser's developer console. In this case the following error is reported:
vega@5?noext:1 ERROR Error: invalid format: %B
I believe that "%B"
is not a valid format code for nominal data. If you remove format='%B'
from the header, the nominal row encoding will work.
来源:https://stackoverflow.com/questions/65837215/altair-ridgeline-doesnt-create-a-plot-with-nominal-groups