Walmart thought shoppers would like the opportunity to use a smartphone app to scan items they want to buy as they walk through store aisles. In theory, they could speed through self-checkout.

But customers couldn't figure out how to work the "Scan & Go" app during tests in 200 stores, so Walmart nixed it.

Instead of looking at the app as a failure, Walmart took what it learned to create another service: It found that customers liked being able to track their spending, an insight that became the impetus for a national program that enables shoppers to store electronic receipts.

"Scan & Go" illustrates how traditional retailers increasingly are using the nimbler approach to innovation that Silicon Valley start-ups are known for. Rather than perfecting a program before rolling it out, they are testing and refining as they go along.

The approach comes as retailers face intense competition for U.S. shoppers, many of whom are still struggling financially. Walmart has had sales declines at its established U.S. stores for more than a year.

"Retailers need to fail often and learn quickly, and adapt and then adopt," said Lori Schafer, executive adviser at SAS Institute, which creates software for retailers.

Here is a look at other Walmart tests and the lessons learned:

Delivery. Walmart is testing same-day delivery of groceries, fresh produce, and other products in San Jose, San Francisco, and Denver. Shoppers select a time slot; their items are delivered on the same day if ordered by 8 a.m. Fees range from $3 to $10.

It is also testing same-day delivery of such merchandise as toys and TVs in Philadelphia, northern Virginia, and Minneapolis if ordered by noon. Customers pay $10 for an unlimited number of items.

In January, Walmart began offering customers the option to order online and pick up their items in stores in Denver.

Wal-Mart Stores Inc., based in Bentonville, Ark., said same-day delivery had been well-received. But in Denver, the pickup option is growing faster than home delivery. Executives reason that shoppers don't want to be holed up at home waiting.

Subscription service. In late 2012, Walmart launched, a mail snack-subscription service that let shoppers taste five to eight different surprise snacks not sold on the discounter's shelves, for a monthly fee of $7. Then it solicited feedback from customers. closed after a year. Analysts said Walmart customers weren't interested in paying for surprise items.

"I think any subscription service . . . has to be aimed at the sweet spot of [Walmart's] shopper - straight-up groceries and toiletries," said Scott Shamberg of TPN, a retail-marketing agency.

Walmart said it learned how to interact with customers and launched an invitation-only review program for the holidays, for input on a curated list of products.

3-D printing. In November, Walmart's U.K. operation, ASDA, began testing 3-D printing technology that allows shoppers to get 8-inch figurines themselves. The cost: 60 pounds, or $100.

Spokesman Russell Craig said the test had been so popular the retailer was considering rolling it out to other stores.