plot = spec.render()
spec = {
// select a point for which to provide details-on-demand
const hover = vl.selectPoint('hover')
.encodings('x') // limit selection to x-axis value
.on('mouseover') // select on mouseover events
.toggle(false) // disable toggle on shift-hover
.nearest(true); // select data point nearest the cursor
// predicate to test if a point is hover-selected
// return false if the selection is empty
const isHovered = hover.empty(false);
// define our base line chart of stock prices
const line = vl.markLine().encode(
vl.x().fieldT('date'),
vl.y().fieldQ('price').scale({type: 'log'}),
vl.color().fieldN('symbol')
);
// shared base for new layers, filtered to hover selection
const base = line.transform(vl.filter(isHovered));
// mark properties for text label layers
const label = {align: 'left', dx: 5, dy: -5};
const white = {stroke: 'white', strokeWidth: 2};
return vl.data('data/stocks.csv')
.layer(
line,
// add a rule mark to serve as a guide line
vl.markRule({color: '#aaa'})
.transform(vl.filter(isHovered))
.encode(vl.x().fieldT('date')),
// add circle marks for selected time points, hide unselected points
line.markCircle()
.params(hover) // use as anchor points for selection
.encode(vl.opacity().if(isHovered, vl.value(1)).value(0)),
// add white stroked text to provide a legible background for labels
base.markText(label, white).encode(vl.text().fieldQ('price')),
// add text labels for stock prices
base.markText(label).encode(vl.text().fieldQ('price'))
)
.width(700)
.height(400);
}
JSON.stringify(spec.toObject(), 0, 2)
Purpose-built for displays of data
Observable is your go-to platform for exploring data and creating expressive data visualizations. Use reactive JavaScript notebooks for prototyping and a collaborative canvas for visual data exploration and dashboard creation.
