+--------+---------+
| Fruit  |  Code   |
+--------+---------+
| Apple  | 1,2,3,4 |
| Orange |     6,7 |
| Banana |      10 |
+--------+---------+

fruitlist = list('Apple' = c(1,2,3,4),
                 'Orange' = c(6,7),
                 'Banana' = c(10)

                 )

> which(fruitlist==10)
Error in which(fruitlist == 10) :
  (list) object cannot be coerced to type 'double'

> which( 10 %in% fruitlist)
[1] 1