absolute function with select of stream query

is there a way to use abs function with a stream query’s select statement?

for e.g.
from t in tA select abs(t)

There could be other ways, but a custom aggregate function did the trick;

aggregate changeSign(float f) returns float{
float s0;
action add(float f) {
log ("add: "+f.toString());
if (f < 0.0) then{
s0:=f *-1.0;

action value() returns float{
	log ("value: "+s0.toString());
	return s0;