Custom order of points drawing a line

[jmansilla]

Hi there folks.
@jakevdp I'm happy I found your comment here #689

ordering of points in a line as well. I used that in an example here: 2098f8d

Right now I'm having trouble drawing a line exactly because of the ordering issue.
My problem is that I have to specify the ordering by providing the values, more or less like this:

alt.Chart(data).mark_line().encode(
        x='x:Q',
        y='y:Q',
        order=alt.Order('topic:N', sort=['Some Topic', 'Amazing Topic', 'Some Other', 'Minor Topic'])
    )

but I'm getting:

altair.vegalite.v2.schema.channels.Order->sort, validating 'anyOf'

['Some Topic', 'Amazing Topic', 'Some Other', 'Minor Topic'] is not valid under any of the given schemas

Is there any workaround for this?

[jakevdp]

The order field can only use ascending or descending... I'm not certain it's currently possible to do what you want in Vega-Lite.

[kanitw]

You can derive a new field and sort by that field e.g., something like:

{
  calculate: "{'Some Topic': 0, 'Amazing Topic': 1, ...}[datum.topic]"
  as: "topic_order"
}

[kanitw]

If you think this custom order should be supported, please file an issue in Vega-Lite repo.

[jmansilla]

Thanks folks.

Solved.

[ihightower]

can someone explain how this is solved clearly with example code. I also want to sort the stacked bars in a custom order. Lower stack say is 'Leave', Middle stack is 'Roster', Upper stack is 'OT' for Work Types. just ascending and descending for sort order doesn't cut it.

[jakevdp]

Currently you can control the stack order using an order encoding, and the legend order using the sort:

import altair as alt
import pandas as pd

df = pd.DataFrame({
    'label': ['Leave', 'OT', 'Roster'],
    'hours': [5, 6, 7]
})

alt.Chart(df).transform_calculate(
    order="{'Leave': 0, 'Roster': 1, 'OT': 2}[datum.label]"
).mark_bar().encode(
    x='hours',
    color=alt.Color('label', sort=['Leave', 'Roster', 'OT']),
    order='order:Q'
)

When vega/vega-lite#1734 is addressed, this will be easier.