ts(x, _id, _tf) {
        if (_tf) return this.tstf(x, _tf, _id)
        let ts = this.env.tss[_id]
        if (!ts) {
            ts = this.env.tss[_id] = [x]
            ts.__id__ = _id
        } else {
            ts[0] = x
        }
        return ts
    }
Creates a new time-series & records each x.
Returns  an array. Id is auto-genrated
@param {*} x - A variable to sample from
@return {TS} - New time-series