plot = {
return Plot.plot({
marks: [
Plot.ruleY([0]),
Plot.lineY(ibm.data, {x: "Date", y: "Close", stroke: d => ibm.data.includes(selectedValue) ? "red": "black"}),
Plot.lineY(goog.data, {x: "Date", y: "Close", stroke: d => goog.data.includes(selectedValue) ? "red": "black"}),
Plot.lineY(ibm.data, Plot.pointer({x: "Date", y: "Close", strokeWidth: 10, stroke: "red"})),
Plot.lineY(goog.data, Plot.pointer({x: "Date", y: "Close", strokeWidth: 10, stroke: "red"})),
]
});
}