Two separate vectors of same length and eliminating items in both vectors, whenever the values of those vectors are the same at identical columns. Depending on this the values of a third vector shall be eliminated accordingly

[lmiq]

julia> idxs = x .!= y
5-element BitVector:
 1
 1
 0
 0
 1

julia> x[idxs]
3-element Vector{Float64}:
 0.1
 0.2
 0.5

julia> y[idxs]
3-element Vector{Float64}:
 0.2
 0.3
 0.6

julia> co[idxs]
3-element Vector{Float64}:
 0.7
 0.8
 1.1