Question, how to divide two aggregate

sorry, I could not find anything in the documentation how to divide two aggregate, I am using this syntax but I am stuck, all I want is to create a new aggregation new, which is the division of two aggregation sum(Installed_qty) and sum(budget)

bar = alt.Chart(df).transform_calculate(
                               new='sum(Installed_qty)'/'sum(budget)'
                                       ).mark_bar().encode(
                                   x=alt.X("date:O", timeUnit="yearmonthdate",axis=alt.Axis(format="%d %b %y")),
                                   y='new:Q'   

[jakevdp]

It’s a bit awkward in the Vega-Lite transform syntax, but you have to create two aggregate transforms and then divide them within a calculate transform. e.g.

bar = alt.Chart(df).transform_aggregate(
    sum_installed='sum(Installed_qty)',
    sum_budget='sum(budget)',
    groupby=['date']
).transform_calculate(
    new='datum.sum_installed / datum.sum_budget'
).mark_bar().encode(
    x=alt.X("date:O", timeUnit="yearmonthdate",axis=alt.Axis(format="%d %b %y")),
    y='new:Q'
)

If you’re using a pandas dataframe, it might be cleaner to add columns with the computed values.

[jakevdp]

You are applying the pts filter after the calculate and aggregate transforms, which is probably not what you want. Transforms are applied in the order they are specified.