Immediately preceding item/s in a list

prev x     prev[x]

Where x is a list, for each item, returns the previous item.

For the first item, it returns a null if the list is vector, otherwise an empty list ().

q)prev 2 3 5 7 11
0N 2 3 5 7
q)prev (1 2;"abc";`ibm)
`int$()
1 2
"abc"

Shift the times in a table:

q)update time:prev time by sym from t

prev is a uniform function.