Walmart is the worlds largest retailer with $469 billion in revenue in 2012. It's online competitor, Amazon, generates only $61 billion but is growing at a faster rate.
Amazon's advantage is in warehousing with dedicated distribution sites that can send a parcel for around half what it costs Walmart. But Walmart are learning and the opening of two huge dedicated distribution centres in the US will make them more competitive.
On the other side of the equation, Amazon have invested in creating pick-up points or locker points for those customers who can't accept deliveries while Walmart have instant pick-up points in their 4,100 stores spread across the US. (A store within 5 miles of 50% of the population)
The comparison is an interesting one even if just to highlight that the mix of Bricks'n'Mortar and online still has a lot of sorting out to do before a stable model can be identified.