How to properly use array and using it as random?

[mybitch 9]

Example.

 

 

setarray .@frate[0],500,600,700,800,900,1000,1100,1200,1300,1400,1500;set $@rate,rand(.@frate);

 

How to use the list of array to be come random for setting $@rate?

[Patskie 88]

set $@rate,.@frate[rand(getarraysize(.@frate))];

[mybitch 9]

Ty!