I have set of active record object in array.
I just want to delete on object from array not in database
a = Model.limit(2)
b = Model.first
a.to_a - [b]
a.to_a convertrs the relation into an array in in memory.
[b] is an array whith just the element, you want to delete (in memory).
a.to_a - [b] does an array substraction.
(In Rails 3.2 .to_a was applied automatically to a relation when it was accessed. I agree with
gregates: It's better to convert the relation to an array explicitly)