roc(src, len, _id) {
        let id = this._tsid(_id, `roc(${len})`)
        return this.ts(
            100 * (src[0] - src[len]) / src[len], id, src.__tf__
        )
    }
Rate of Change
@param {TS} src - Input
@param {number} len - Length
@return {TS} - New time-series