Tooltip with Multi-Series Line Chart in Vega-Lite API - d3.js

Question

I am trying to recreate this example in Vega-Lite API in an Observable notebook. I am able to recreate the ruler with the multiple line series from another example in Observable. But I am having trouble adding tooltips, I would like to add the symbol ticker and the price of the stock. Here is my Observable notebook. Where would I put the tooltip specifications? Thanks!
plot = {
// select a point for which to provide details-on-demand
const hover = vl.selectSingle()
.encodings('x') // limit selection to x-axis value
.on('mouseover') // select on mouseover events
.nearest(true) // select data point nearest the cursor
.empty('none'); // empty selection includes no data points
// define our base line chart
const line = vl.markLine()
.data(stocks)
.encode(
vl.x().fieldT('date'),
vl.y().fieldQ('price'),
vl.color().fieldN('symbol'),
);
// shared base for new layers, filtered to hover selection
const base = line.transform(vl.filter(hover));
return vl.data(stocks)
.layer(
line,
// add a rule mark to serve as a guide line
vl.markRule({color:'#c0c0c0'})
.transform(
vl.filter(hover),
vl.pivot({pivot: 'symbol', value: 'price', groupby: ['date']}))
.encode(vl.x().fieldT('date'),
vl.tooltip().fieldQ('price')),
// add circle marks for selected time points, hide unselected points
line.markCircle()
.select(hover) // use as anchor points for selection
.encode(vl.opacity().if(hover, vl.value(1)).value(0),
vl.tooltip(['symbol','price']))
)
.render(); }

Answer 1

Here's how you use pivot on that example
vl.pivot('symbol').value('price').groupby( ['date']))
The pivot there helps you getting the data into table format, so you can have all the symbol prices available in one row. Here is a full working example of a Vega-Lite API multi-line series chart with tooltips:
https://observablehq.com/#vega/multi-series-line-chart-with-tooltip