Altair Heatmap Ticks Text

Is there a way to set the ticks text to a list of strings? I know that ideally it is best to have the ticks directly in the dataset but unfortunately this is not always possible or

Solution 1:

One way to do this is to use the labelExpr axis attribute, which allows defining new label values using the Vega Expression syntax. For example:

alt.Chart(source).mark_rect().encode(
    alt.X('x:O',
      axis=alt.Axis(
        values=[2*i*np.pi for i inrange(5)],
        labelExpr="round(datum.value / PI) + 'π'"
      )
    ),
    alt.Y('y:O',
      axis=alt.Axis(
        labelExpr="round(datum.value / PI) + 'π'"
      )
    ),
    color='z:Q'
)