wpr(len, _id, _tf) {
        let id = this._tsid(_id, `wpr(${len})`)
        let tfs = _tf || ''
        let high = this.env.shared[`high${tfs}`]
        let low = this.env.shared[`low${tfs}`]
        let close = this.env.shared[`close${tfs}`]

        let hh = this.highest(high, len, id)
        let ll = this.lowest(low, len, id)

        let res = (hh[0] - close[0]) / (hh[0] - ll[0])
        return this.ts(-res * 100 , id, _tf)
    }
Williams %R
@param {number} len - length
@return {TS} - New time-series