vl_spec = ({
"data": {
"name": "SOURCE",
"values": {
"nested": [
{"key": "alpha", "foo": [1, 2], "bar": ["A", "B"]},
{"key": "beta", "foo": [3, 4, 5], "bar": ["C", "D"]}
]
},
"format": {"property": "nested"}
},
"transform": [{"flatten": ["foo", "bar"]}],
"mark": "circle",
"encoding": {
"x": {"field": "foo", "type": "quantitative"},
"y": {"field": "bar", "type": "nominal"},
"color": {"field": "key", "type": "nominal"}
}
})