Variance

var x    var[x]

Where x is a numeric list, returns its variance as a float atom. Nulls are ignored.

q)var 2 3 5 7
3.6875
q)var 2 3 5 0n 7
3.6875
q)select var price by sym from trade where date=2010.10.10,sym in`IBM`MSFT

var is an aggregate function, equivalent, where sqr:{x*x} to

{avg[sqr x]-sqr[avg x]}