Chart-Title from data values

[joerg55]

Hi community,

I know this is not necessarily a question for this forum, but I hope someone might be able to help. I want to take the title of my chart directly from the data which are base of the chart. For example the title of this chart should be 'charttitle':

{
"$schema": "https://vega.github.io/schema/vega-lite/v5.json",
"data": {
"values": [
{"quater":"1", "sales":"100", "title":"charttitle"},
{"quater":"2", "sales":"200", "title":"charttitle"},
{"quater":"3", "sales":"300", "title":"charttitle"},
{"quater":"4", "sales":"400", "title":"charttitle"}
]
},

"mark": "bar",
"encoding": {
"x": {"field": "quater", "type":"ordinal"},
"y": {"field": "sales", "type": "quantitative"},
},
"title": ???
}

How can I achieve this?

[Marco_Liberati]

Hi @joerg55

I think the best option here is to define a transform of the data and reduce the data into a single value to use as title.

[joerg55]

Hi Marco,

that is exactly what I try to do. In pseudo code it could look like this:

• "title": (select title from data limit 1); or in standard sql

• "title": (select top 1 title from data)

but how can i achieve that in vega?

[Marco_Liberati]

In Vega that is a bit tricky, as it requires to add alongside the query data, also another dataset derived from it with the usage of a transform.
The transform object can apply different types of aggregations in Vega, probably a combination of a window + filter would be a good starting point: Transforms | Vega

[joerg55]

@Marco,

thank you very much for your help. I already took a look to the transform.window option and the possibility to isolate a single value by an appropriate filter (e. g. 'rank <= 1'). My main problem is to assign this single value (which is an object in vega?) to the title of the chart