neg(x, _id) {
        let id = this._tsid(_id, `neg`)
        let x0 = this.na(x) ? NaN : (x.__id__ ? x[0] : x)
        return this.ts(-x0, id, x.__tf__)
    }
Returns a negative value / time-series
@param {(TS|*)} x - Input
@return {TS} - New time-series