In a play for scale in a rapidly expanding e-commerce market, Vantiv Inc. on Wednesday agreed to buy the United Kingdom-based processor Worldpay Group plc for approximately $9.9 billion. JPMorgan Chase & Co., which had also expressed interest in Worldpay, has withdrawn from the bidding. The boards of the two companies announced an “agreement in principle” calling for Vantiv to pay almost $5, at current exchange rates, for each Worldpay share. That figure includes a dividend payment of about 6 cents per share. The deal values Worldpay at a premium of about 20.7% to the company’s closing price on June 30, before takeover speculation lifted its shares.