Function lttbSample

src/data/lttbSample.ts:177–212

(
  data: ReadonlyArray<DataPoint> | Float32Array,
  targetPoints: number
)

export function lttbSample(data: DataPoint[], targetPoints: number): DataPoint[];
export function lttbSample(data: ReadonlyArray<DataPoint>, targetPoints: number): ReadonlyArray<DataPoint>;
export function lttbSample(
  data: ReadonlyArray<DataPoint> | Float32Array,
  targetPoints: number
): ReadonlyArray<DataPoint> | Float32Array {
  const threshold = Math.floor(targetPoints);

  if (data instanceof Float32Array) {
    const n = data.length >>> 1;
    if (threshold <= 0 || n === 0) return new Float32Array(0);

    // If we're already under the target, avoid copying.
    if (n <= threshold) return data;

    const indices = lttbIndicesForInterleavedXY(data, threshold);
    const out = new Float32Array(indices.length * 2);
    for (let i = 0; i < indices.length; i++) {
      const idx = indices[i]!;
      out[i * 2 + 0] = data[idx * 2 + 0];
      out[i * 2 + 1] = data[idx * 2 + 1];
    }
    return out;
  }

  const n = data.length;
  if (threshold <= 0 || n === 0) return [];

  // Story requirement: when data is shorter than the target, return original.
  if (n <= threshold) return data;

  const indices = lttbIndicesForDataPoints(data, threshold);
  const out = new Array<DataPoint>(indices.length);
  for (let i = 0; i < indices.length; i++) {
    out[i] = data[indices[i]!]!;
  }
  return out;
}