Why does this Vega-lite code fail to display a chart? It uses a transform lookup to join tables and one of the fields from the second table is used in the legend.
{
"data": {
"values": [
{"group": 1, "person": "Alan"},
{"group": 1, "person": "George"},
{"group": 1, "person": "Fred"},
{"group": 2, "person": "Steve"},
{"group": 2, "person": "Nick"},
{"group": 2, "person": "Will"},
{"group": 2, "person": "Cole"},
{"group": 3, "person": "Rick"},
{"group": 3, "person": "Tom"}
]},
"transform": [
{
"lookup": "person",
"from": {
"data": {
"values": [
{"name": "Alan", "_source": { "age": 10, "category": 15}},
{"name": "Tom", "_source": { "age": 7, "category": 35}},
{"name": "Fred", "_source": { "age": 17, "category": 75}}
]},
"key": "name",
"fields": ["_source.age", "_source.category"]
}
},
{"calculate": "datum.person+' '+datum._source.category", "as": "legend"},
{"aggregate":
[{"op": "sum", "field": "_source.age", "as": "totalage"}],
"groupby": ["totalage", "legend", "_source.category"]}
],
"mark": "bar",
"encoding": {
"x": {"field": "_source.category", "type": "ordinal"},
"y": {"field": "totalage", "type": "quantitative"},
"color": {
"field": "legend",
"title": "My Legend",
"legend": {"orient": "top", "columns": 3}
}
}
}
But this Vega-lite code succeeds in displaying a chart? It uses a transform lookup to join tables and none of the fields from the second table are used in the legend.
{
"data": {
"values": [
{"group": 1, "person": "Alan"},
{"group": 1, "person": "George"},
{"group": 1, "person": "Fred"},
{"group": 2, "person": "Steve"},
{"group": 2, "person": "Nick"},
{"group": 2, "person": "Will"},
{"group": 2, "person": "Cole"},
{"group": 3, "person": "Rick"},
{"group": 3, "person": "Tom"}
]},
"transform": [
{
"lookup": "person",
"from": {
"data": {
"values": [
{"name": "Alan", "_source": { "age": 10, "category": 15}},
{"name": "Tom", "_source": { "age": 7, "category": 35}},
{"name": "Fred", "_source": { "age": 17, "category": 75}}
]},
"key": "name",
"fields": ["_source.age", "_source.category"]
}
},
{"calculate": "datum.person+' '+datum.group", "as": "legend"},
{"aggregate":
[{"op": "sum", "field": "_source.age", "as": "totalage"}],
"groupby": ["totalage", "legend", "_source.category"]}
],
"mark": "bar",
"encoding": {
"x": {"field": "_source.category", "type": "ordinal"},
"y": {"field": "totalage", "type": "quantitative"},
"color": {
"field": "legend",
"title": "My Legend",
"legend": {"orient": "top", "columns": 3}
}
}
}
The issue is in the line
{"calculate": "datum.person+' '+datum._source.category", "as": "legend"}
This says to look for the category attribute of datum._source. But your data does not have a column named "_source", it has a column named "_source.category".
To fix it, you can reference the column like this:
{"calculate": "datum.person+' '+datum['_source.category']", "as": "legend"}