Vega lite: having two separate datasets with separate filters - vega-lite

Question

I was wondering how I could have a sort of hconcat in vega lite, but with two separate datasets. I want to have the top 10 and lower 10 values displayed next to each other with different constraints but I am having issues with the filter.

Answer 1

Data and transforms can be specified at any level of the chart, and they are passed down to subcharts when applicable. Here is an example adapted from Filtering Top K Items in the example gallery, which applies a different filter to each concatenated chart (view in editor):
{
"data": {
"values": [
{"student": "A", "score": 100},
{"student": "B", "score": 56},
{"student": "C", "score": 88},
{"student": "D", "score": 65},
{"student": "E", "score": 45},
{"student": "F", "score": 23},
{"student": "G", "score": 66},
{"student": "H", "score": 67},
{"student": "I", "score": 13},
{"student": "J", "score": 12},
{"student": "K", "score": 50},
{"student": "L", "score": 78},
{"student": "M", "score": 66},
{"student": "N", "score": 30},
{"student": "O", "score": 97},
{"student": "P", "score": 75},
{"student": "Q", "score": 24},
{"student": "R", "score": 42},
{"student": "S", "score": 76},
{"student": "T", "score": 78},
{"student": "U", "score": 21},
{"student": "V", "score": 46}
]
},
"transform": [
{
"window": [{"op": "rank", "as": "rank"}],
"sort": [{"field": "score", "order": "descending"}]
}
],
"vconcat": [
{
"transform": [{"filter": "datum.rank <= 3"}],
"mark": "bar",
"encoding": {
"x": {"field": "score", "type": "quantitative"},
"y": {
"field": "student",
"type": "nominal",
"sort": {"field": "score", "op": "average", "order": "descending"}
}
}
},
{
"transform": [{"filter": "datum.rank > 19"}],
"mark": "bar",
"encoding": {
"x": {"field": "score", "type": "quantitative"},
"y": {
"field": "student",
"type": "nominal",
"sort": {"field": "score", "op": "average", "order": "descending"}
}
}
}
]
}
Similarly, if you wanted a different data source in each subchart, you could specify the "data" property in the subcharts.