Method downSample

src/data/DataStore.ts:1038–1090

* Large data down sampling on given dimension * @param sampleIndex Sample index for name and id

(
        dimension: DimensionIndex,
        rate: number,
        sampleValue: (frameValues: ArrayLike<ParsedValue>) => ParsedValueNumeric,
        sampleIndex: (frameValues: ArrayLike<ParsedValue>, value: ParsedValueNumeric) => number
    )

     * @param sampleIndex Sample index for name and id
     */
    downSample(
        dimension: DimensionIndex,
        rate: number,
        sampleValue: (frameValues: ArrayLike<ParsedValue>) => ParsedValueNumeric,
        sampleIndex: (frameValues: ArrayLike<ParsedValue>, value: ParsedValueNumeric) => number
    ): DataStore {
        const target = this.clone([dimension], true);
        const targetStorage = target._chunks;

        const frameValues = [];
        let frameSize = Math.floor(1 / rate);

        const dimStore = targetStorage[dimension];
        const len = this.count();
        const rawExtentOnDim = target._rawExtent[dimension] = initExtentForUnion();

        const newIndices = new (getIndicesCtor(this._rawCount))(Math.ceil(len / frameSize));

        let offset = 0;
        for (let i = 0; i < len; i += frameSize) {
            // Last frame
            if (frameSize > len - i) {
                frameSize = len - i;
                frameValues.length = frameSize;
            }
            for (let k = 0; k < frameSize; k++) {
                const dataIdx = this.getRawIndex(i + k);
                frameValues[k] = dimStore[dataIdx];
            }
            const value = sampleValue(frameValues);
            const sampleFrameIdx = this.getRawIndex(
                Math.min(i + sampleIndex(frameValues, value) || 0, len - 1)
            );
            // Only write value on the filtered data
            (dimStore as number[])[sampleFrameIdx] = value;

            if (value < rawExtentOnDim[0]) {
                rawExtentOnDim[0] = value;
            }
            if (value > rawExtentOnDim[1]) {
                rawExtentOnDim[1] = value;
            }

            newIndices[offset++] = sampleFrameIdx;
        }

        target._count = offset;
        target._indices = newIndices;

        target._updateGetRawIdx();

        return target;
    }

    /**
     * Data iteration