Vega-Lite chart from OECD API - json

Question

I have an api which I would like to use directly within Vegalite, in order for the chart to update automatically.
https://stats.oecd.org/SDMX-JSON/data/REVGBR/TOTALTAX.NES/all?startTime=1965&endTime=2021&dimensionAtObservation=allDimensions
However the api doesn't seem to be in a pleasant format.
{
"$schema": "https://vega.github.io/schema/vega-lite/v5.2.json",
"data": {
"url": "https://stats.oecd.org/SDMX-JSON/data/REV/NES.TOTALTAX.TAXGDP.OAVG?contentType=json",
"format": {
"type": "json",
"property": "dataSets[0].series['0:0:0:0'].observations"
},
"transform": [
{
"type": "formula",
"as": "year",
"expr": "parseInt(datum.key)"
},
{
"type": "formula",
"as": "Tax_revenue",
"expr": "datum.value[0]"
}
]
},
"mark": "line",
"encoding": {
"x": {"field": "year", "type": "temporal"},
"y": {"field": "Tax_revenue", "type": "quantitative"}
}
}
When looking at the data viewer, all that is shown is the values, without the years.
The values however are not clean, e.g. [24.855,null]
Is it even possible to get this api to work within vegalite?

Answer 1

It is possible but you need to make assumptions. As you know the query to the API starts with 1965, you can use something like this assuming the years are continuous.
{
"$schema": "https://vega.github.io/schema/vega-lite/v5.2.json",
"data": {
"name": "api",
"url": "https://stats.oecd.org/SDMX-JSON/data/REV/NES.TOTALTAX.TAXGDP.OAVG?contentType=json",
"format": {
"type": "json",
"property": "dataSets[0].series['0:0:0:0'].observations"
}
},
"transform": [
{"fold": ["0", "1", "2", "3","4","5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "50", "51", "52", "53", "54", "55"]},
{"calculate": "parseInt( datum.key) + 1965", "as": "year"},
{"calculate": "datum.value[0]", "as": "Tax_revenue"}
],
"mark": "line",
"encoding": {
"x": {"field": "year", "type": "nominal"},
"y": {"field": "Tax_revenue", "type": "quantitative"}
}
}