Functions on NULLs

If used in the arguments of aggregate functions such as sum/avg/med, NULL values are ignored.

$ x = 1 2 NULL NULL 3;
$ log x;
[0,0.693147,,,1.098612]

$ x = 1 2 NULL NULL 3;
$ avg x;
2

$ sum x;
6

$ med x;
2

$ x=1..3;
$ move(x,3);
[,,]

$ prev 1 2 3;
[,1,2]

$ next 1 2 3;
[2,3,]