Show more timestamp ticks in altair

Question

Here is a toy example of my data along with the code I am working with

import altair as alt
import numpy as np
import pandas as pd

np.random.seed(0)
df = pd.DataFrame({
        'grp': np.random.choice(['A','B'],100, p=[0.5,0.5]),
        'dur': np.random.randint(350, 1250, 100),
    })
alt.Chart(df).mark_boxplot().encode(
    x=alt.X('grp:N', title='Group'),
    y=alt.Y('dur:T', title='Duration', axis=alt.Axis(format="%S.%L", tickCount=5)), 
).properties(width=100)

I am getting only two ticks on the Y-axis, i.e. 0.800, 1.200 which is in seconds:milliseconds format. I am unable to include the resulting plot because of insufficient reputation. I want smaller time steps in milliseconds the axis ticks such as 0.200, 0.400, 0.600, 0.800, 1.000, 1.200. Can someone please help me get it?

The tickCount option doesn't change anything.

joelostblom · Answer

It seems like neither of tickCount, values, or alt.Scale(zero=True) work as expected with a temporal axis, but if you are ok with changing the axis type to quantitative and dividing your input values, you can get this plot:

import altair as alt
import numpy as np
import pandas as pd

np.random.seed(0)
df = pd.DataFrame({
        'grp': np.random.choice(['A','B'],100, p=[0.5,0.5]),
        'dur': np.random.randint(350, 1250, 100) / 1000,
    })
alt.Chart(df).mark_boxplot().encode(
    x=alt.X('grp:N', title='Group'),
    y=alt.Y('dur:Q', title='Duration', axis=alt.Axis(format=".3f")), 
).properties(width=100)

Show more timestamp ticks in altair

1 Answers