Setting tick labels to list of strings

Hi everyone,

Is there a way to set the tick labels in a chart to some list of strings? Here is the chart:

df=pd.DataFrame({'days_between': [1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6],
                 'person': [1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2,2],
                 'value': [10,11,12,13,14,15,10,11,12,13,14,15]})

alt.Chart(df).mark_square(size=400).encode(
    x=alt.X('days_between:Q', axis=alt.Axis(values=[1,2,3,4,5,6])),
    y=alt.Y('person:Q', axis=alt.Axis(values=[1,2])),
    color=alt.Color('value:Q', scale=alt.Scale(range=['green','yellow','red']))).properties(width=400, height=400).interactive()

I would have thought this would work (similar to matplotlib in some sense):

 alt.Axis(..., labels=['string 1', 'string 2', 'string 3', 'string 4', 'string 5', 'sting 6'])

Is there a way to do this when using quantitative data types as I am in the above example?

[palewire]

Am I able to do this with date values ala:

axis=alt.Axis(values=[date(2008, 9, 1)]),

[jakevdp]

Altair is designed to properly display whatever data you input regardless of the type, unlike matplotlib which requires you to input quantitative data and then manually re-map the axes to whatever non-quantitative data you want it to represent.

So I’d say the best approach to this for Altair is to actually use the values of interest within the dataset itself, and then no manual axis label mapping will be necessary.

For example:

df=pd.DataFrame({'days_between': [1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6],
                 'person': [1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2,2],
                 'value': [10,11,12,13,14,15,10,11,12,13,14,15]})
df['days_between'] = df['days_between'].map({i + 1: 'ABCDEF'[i] for i in range(6)})

alt.Chart(df).mark_square(size=400).encode(
    x=alt.X('days_between:O'),
    y=alt.Y('person:Q', axis=alt.Axis(values=[1,2])),
    color=alt.Color('value:Q', scale=alt.Scale(range=['green','yellow','red']))
).properties(width=400, height=400).interactive()