Sample variance

svar x    svar[x]

Where x is a numeric list, returns its sample variance as a float atom.

q)var 2 3 5 7
3.6875
q)svar 2 3 5 7
4.916667
q)select svar price by sym from trade where date=2010.10.10,sym in`IBM`MSFT

svar is an aggregate function, equivalent to {var[x]*count[x]%-1+count x}.