How to hide individual staff lines in lilypond?

Question

How can individual staff lines be hidden in lilypond?

E.g. in

\new DrumStaff \with {
  \override StaffSymbol.line-count = #3
}
<<
  \drummode {
    <<
      {
        r4 hh 
      } \\
      {
        bd4 bd8 bd8 
      }
    >>
  }
>>

I'd like to hide the staff line in the middle.

And e.g. in

\new DrumStaff \with {
  \override StaffSymbol.line-count = #2
}
<<
  \drummode {
    <<
      {
        r4 hh 
      } \\
      {
        bd4 bd8 bd8 
      }
    >>
  }
>>

I'd like to hide the staff line at the very top (only visible when there is a note at the top) and the staff line at the very bottom (only visible when there is a note at the bottom)

I took a look at the documentation, but could only find how to hide all of the staff lines, but not individual ones.

Answer 1

I don't fully understand what you're looking for in the bottom example. Feel free to clarify, or perhaps this answer will move you in the right direction.

This solution specifies the number of staff lines while also specifying their positions.

\version "2.18.2"

\relative c' {
  \new DrumStaff 
    <<
      \drummode {
        \override Staff.StaffSymbol.line-count = #2
        \override Staff.StaffSymbol.line-positions = #'(-2 2)
        <<
          {
            r4 hh 
          }
          \\
          {
            bd4 bd8 bd8 
          }
        >>
      }
    >>
}