Understanding Standard Method Utilization within a Controller Class

Nice to meet you.I'm a beginner at ruby.
I am trying to create a web system using ruby on rails.
There was an error that could not be resolved, so I would like to ask you a question.

in the controller class you created
String type string retrieved from DB using ransack I want to split using split method, but I can't do it well.

The error message is as follows:

 undefined local variable or method `"' for #
<HogeController:0x007f9529648cf8>

The source code is as follows:

def index
  @q = Hoge.search (params[:q])
  @[email protected](distinct:true)
  @hoges.each do|a|
  str=a.hogestr.to_s.split(",")
  end
end

Thank you for your cooperation.