Years Not Formatting to Correct Date Format - vega-lite

Question

Fairly new to vega/vega-lite and javascript in general so trying my hand at this and it is not working the way I'd like.
My main issue at the moment is that my years are whole numbers as primitive values. I've tried parsing them to show as temporal units in the format of %Y but I just keep getting decimal places which doesn't work.
{
"data": {"name": "dataset"},
"width": 500,
"height": 500,
"layer": [
{
"mark": {
"type": "line",
"point": true
},
"encoding": {
"y": {"aggregate": "mean","field": "Index Score", "type": "quantitative", "axis": {"format": ".1e"}, "title": "Economic Exposure Score"},
"x": {"field": "Year","type": "quantitative", "title": "Years"},
"color": {"field": "Country", "type": "nominal", "legend": null}
}
},
{
"mark": {"type": "text", "align": "center", "dy": 15, "fontWeight": "bold", "fontSize": 14},
"encoding": {
"x": {
"field": "Year",
"type": "quantitative"
},
"y": {
"field": "Index Score",
"type": "quantitative"
},
"text": {"field": "Event Name", "type": "nominal"},
"color": {"value": "black"}
}
}
]
}
Here is where I'm at right now: v1 index score over years. Yes there are a lot of lines. I have a dynamic card that will show the chart only once a country has been selected from a slicer in the dashboard so no worries there. I plan on adding labels to the lines.
Summary of troubleshooting:
have tried formatting this at the "Data" level as well as within the mark/line/encoding/y but I either get a whole number representation or a decimal...

Answer 1

Option 1: Create the date in Power Query
As you say in the comments, you can easily create the date on the Power BI side and pass it in. I would have your month and year columns as text and concatenate them like this:
let
Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
#"Changed Type" = Table.TransformColumnTypes(Source,{{"Country", type text}, {"Index Score", type number}, {"Month", type text}, {"Event Name", type any}, {"Year", type text}}),
#"Added Custom" = Table.AddColumn(#"Changed Type", "Date", each [Month] & " 1, " & [Year], type text),
#"Changed Type1" = Table.TransformColumnTypes(#"Added Custom",{{"Date", type date}}),
#"Calculated End of Month" = Table.TransformColumns(#"Changed Type1",{{"Date", Date.EndOfMonth, type date}})
in
#"Calculated End of Month"
If you want start of month, remove the #"Calculated End of Month" step.
Option 2: Formatting in Vega-lite
You could also leave the year as you have it, and simply add formatting in the x-axis encoding in Vega:
"encoding": {
"x": {
...
"axis": {"format": "0000"}
},
Open the Chart in the Vega Editor