Take a look at this video of a robotic hydroponic lettuce farm in Belgium. With appropriate techniques, companies are able to grow lettuce in large indoor fields where crops are sorted, planted, and grown automatically.
(Automated lettuce hydroponics)
..the robotics systems used are from Hortiplan, a horticultural automation company based out of the Netherlands. The hydroponic rows you see being filled and maneuvered are part of their Mobile Gully System. The MGS not only plants the lettuce and arranges it in the field, it also moves the crop along as it develops, and delivers it to the right part of the greenhouse for harvest. That picking is done by hand.
Hortiplanís MGS uses whatís known as the nutrient film technique. Essentially, the gullies (trays) have a very thin layer of nutrient rich water flowing through them. That water is pumped to one end of the field and then flows downhill (thereís a very slight slope on the trays). Lettuce is continually watered, slowly moved across the field by the MGS, which also increases the spaces between gullies so the plants have room to grow. By the time they reach the far end theyíre ready for harvest.
Fans of the 1972 movie Silent Running will also remember (as Peter Jacobs did in the comments) that Bruce Dern took tended his garden with the help of robots.