I have a variable named S_Kx, S_Jx S_Yx, S_Sx

I want to nix all variables that dont' have the same beginning as they do with after _ (i.e. S_Sx would be kept, but S_Kx and all others would be dropped)

therefore

v_vx would be kept

!v_vx would be dropped

v can be ANY letter of the alphabet

how could I approach this?