What is the relationship between grocery and Walmart in the context of the input sentence. Choose an answer from: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

- The Wall Street Journal Asda shocked the grocery trade yesterday by reporting its worst sales performance since it was taken over by Walmart 16 years ago, with discounters continuing to poach its customers.

Answer: operator