altair, set axis step to 1d

Question

This is a simple altar viz:

alt.Chart(df).mark_area().encode(
    x="date:T",
    y="value:Q",
)

I would like to have all days on X axis. On viz you can see Sat 3, Wed 07 but I would like to have Thu 01, Fri 02, Sat 03 and so on.

( end of the question )

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I put here the whole minimal reproducible sample:

import altair as alt
import pandas as pd

# random data
l = [ 3,4,6,7,8,9,12,34,54,65,56,76,87,77,90 ] 
data ={
    'date': [ f'2022-09-{d:02d}' for d in range(1,31) ],
    'value': l + list(reversed(l)),
}
df = pd.DataFrame(data)

# viz
alt.Chart(df).mark_area().encode(
    x="date:T",
    y="value:Q",
)

Also, I write here that I have tried. I have tried unsuccessfully with several options like to include format, change angle or change size.

Answer 1

I think something like the following:

import altair as alt
import pandas as pd

# random data
l = [ 3,4,6,7,8,9,12,34,54,65,56,76,87,77,90 ] 
data ={
    'date': [ f'2022-09-{d:02d}' for d in range(1,31) ],
    'value': l + list(reversed(l)),
}
df = pd.DataFrame(data)

# viz
alt.Chart(df).mark_area().encode(
    
    x=alt.X('date:O', axis=alt.Axis(format='' , labelExpr='date(datum.label) + " " + dayAbbrevFormat(day(datum.label))' ,title='date')),
    y="value:Q",
)