How do I add secondary Y axis in vega-lite with 2 series having the same scale? - vega-lite

Question

I'm trying to build something like this:
example histogram with multiple independent series
I have 2 independent y-axis with orient left and right.
All series/layers using "orient":"right" should be sharing the same scale and all series/layers using "orient":"left" should be sharing the same scale.
I know of the "resolve" option as documented here but having read this How do I add a secondary Y axis to my vega-lite chart? and a bunch of other questions I couldn't find my particular use case.
My futile attempt so far looks like this:
example in online editor
example screenshot
{
"$schema": "https://vega.github.io/schema/vega-lite/v2.json",
"data": {"url": "data/movies.json"},
"transform":[
{"calculate":"datum.Production_Budget * 0.5","as":"y2"}
],
"layer":[
{
"mark": "bar",
"encoding": {
"x": {
"bin": true,
"field": "IMDB_Rating",
"type": "quantitative"
},
"y": {
"axis":{"orient":"left","title":"# of movies","grid":false},
"aggregate": "count",
"type": "quantitative"
}
}},
{
"mark": "line",
"encoding": {
"x": {
"bin": true,
"field": "IMDB_Rating",
"type": "quantitative"
},
"y": {
"field":"Production_Budget",
"aggregate": "average",
"type": "quantitative",
"axis":{"orient":"right","format":"s","title":"avg production budget in $"}
}
}
},
{
"mark": "line",
"encoding": {
"x": {
"bin": true,
"field": "IMDB_Rating",
"type": "quantitative"
},
"y": {
"field":"y2",
"aggregate": "average",
"type": "quantitative",
"axis":{"orient":"right","format":"s","title":"avg production budget in $"}
}
}
}
]
,"resolve": {
"scale":{"y":"independent"}
}
}
I've tried playing with the resolve option:
"resolve": {
"scale":{"axisLeft":"independent"}
}
"resolve": {
"axisLeft":{"y":"independent"}
}
"resolve": {
"axis":{"left":"independent"}
}
but none of them work.

Answer 1

You can do this by creating a layer within a layer: the two orient: "right" charts in a single layer with a shared axis, and the orient: "left" chart with an independent scale:
vega editor link
{
"$schema": "https://vega.github.io/schema/vega-lite/v2.json",
"data": {"url": "data/movies.json"},
"transform": [{"calculate": "datum.Production_Budget * 0.5", "as": "y2"}],
"layer": [
{
"mark": "bar",
"encoding": {
"x": {"bin": true, "field": "IMDB_Rating", "type": "quantitative"},
"y": {
"axis": {"orient": "left", "title": "# of movies", "grid": false},
"aggregate": "count",
"type": "quantitative"
}
}
},
{
"layer": [
{
"mark": "line",
"encoding": {
"x": {"bin": true, "field": "IMDB_Rating", "type": "quantitative"},
"y": {
"field": "Production_Budget",
"aggregate": "average",
"type": "quantitative",
"axis": {
"orient": "right",
"format": "s",
"title": "avg production budget in $"
}
}
}
},
{
"mark": "line",
"encoding": {
"x": {"bin": true, "field": "IMDB_Rating", "type": "quantitative"},
"y": {
"field": "y2",
"aggregate": "average",
"type": "quantitative",
"axis": {
"orient": "right",
"format": "s",
"title": "avg production budget in $"
}
}
}
}
]
}
],
"resolve": {"scale": {"y": "independent"}}
}