Walmart Inc. has created a formidable e-commerce business by investing billions to hire engineers and data scientists, building automated distribution centers tailored for web orders and rolling out curbside pickup for online grocery orders at more than 2,000 stores. The retailer generated $11.5 billion in online sales last year in the U.S., and a redesigned website that better showcases apparel and home decor is expected to boost that total by 40 percent in 2018.