A trend line and a forecast

'chart-trend-forecast': () => ({
  rows: [], config: {},
  foot: [
    'the top chart fits a least-squares trend straight through the points and carries it on past the last day as a dashed forecast',
    'the bottom chart takes the same series and marks the day a change went live with a vertical event flag, above a mean line read from the data',
    'the data is one clean, sorted point per day, which is what a fit needs to draw a line and project it',
    'both read the grid’s filtered rows, so narrowing the grid refits the trend and moves the mean',
  ],
  mount: mountGridCharts({
    rows: trendRows(), columns: trendCols, columnsPer: 1, chartHeight: 280, height: 760,
    charts: [
      {
        type: 'line', x: 'day', y: 'active', full: true, paneHeight: 280,
        trend: { method: 'linear', forecast: 8 },
        title: 'The trend, projected ahead',
      },
      {
        type: 'line', x: 'day', y: 'active', full: true, paneHeight: 280,
        annotations: [
          { kind: 'event', value: 22, label: 'Feature launch' },
          { kind: 'line', compute: 'mean', label: 'Average', axis: 'left' },
        ],
        title: 'The same series, with the launch marked',
      },
    ],
  }),
}),