function lttbDecimation()

in Hands-on lab/lab-files/starter-project/NorthwindMVC/wwwroot/lib/Chart.js/chart.js [9455:9500]

• 46 lines of code
• 7 McCabe index (conditional complexity)

function lttbDecimation(data, start, count, availableWidth, options) {
  const samples = options.samples || availableWidth;
  if (samples >= count) {
    return data.slice(start, start + count);
  }
  const decimated = [];
  const bucketWidth = (count - 2) / (samples - 2);
  let sampledIndex = 0;
  const endIndex = start + count - 1;
  let a = start;
  let i, maxAreaPoint, maxArea, area, nextA;
  decimated[sampledIndex++] = data[a];
  for (i = 0; i < samples - 2; i++) {
    let avgX = 0;
    let avgY = 0;
    let j;
    const avgRangeStart = Math.floor((i + 1) * bucketWidth) + 1 + start;
    const avgRangeEnd = Math.min(Math.floor((i + 2) * bucketWidth) + 1, count) + start;
    const avgRangeLength = avgRangeEnd - avgRangeStart;
    for (j = avgRangeStart; j < avgRangeEnd; j++) {
      avgX += data[j].x;
      avgY += data[j].y;
    }
    avgX /= avgRangeLength;
    avgY /= avgRangeLength;
    const rangeOffs = Math.floor(i * bucketWidth) + 1 + start;
    const rangeTo = Math.min(Math.floor((i + 1) * bucketWidth) + 1, count) + start;
    const {x: pointAx, y: pointAy} = data[a];
    maxArea = area = -1;
    for (j = rangeOffs; j < rangeTo; j++) {
      area = 0.5 * Math.abs(
        (pointAx - avgX) * (data[j].y - pointAy) -
        (pointAx - data[j].x) * (avgY - pointAy)
      );
      if (area > maxArea) {
        maxArea = area;
        maxAreaPoint = data[j];
        nextA = j;
      }
    }
    decimated[sampledIndex++] = maxAreaPoint;
    a = nextA;
  }
  decimated[sampledIndex++] = data[endIndex];
  return decimated;
}