Julia conditional assignment based on | (or) in multidimensional array - arrays

Question

I have a 3D array, and based on the values in one "row" using the or operator "|", I would like to substitute values in a different row. I've attempted to build a mwe, here goes:
# create new array
Pop = fill(Int8(3), 1, 3, 4)
# change values in one row of array
Pop[:,:,2] = [5,6,7]
# change values in second row of array
Pop[:,:,4] = [9,10,11]
# attempt conditional substitution, if element-wise value of Pop[:,:,2] equals either 6 or 7, then substitute the corresponding element wise (across row in dimension 3) for 8
Pop[:,:,2] == 6|7 Pop[:,:,3] .= 8
# to produce this end result
Pop[:,:,3] = [3,8,8]
Pop
I'm missing something in the syntax for the substitution. Thx. J

Answer 1

This works, but requires a temporary variable.
julia> temp = Pop[:,:,3]
1×3 Array{Int8,2}:
3 3 3
julia> temp[(Pop[:,:,2] .== 6) .| (Pop[:,:,2] .== 7)] .= 8
2-element view(::Array{Int8,1}, [2, 3]) with eltype Int8:
8
8
julia> Pop[:,:,3] = temp
1×3 Array{Int8,2}:
3 8 8

Answer 2

I think it's clearer to separate the stages:
julia> Pop = fill(Int8(3), 1, 3, 4);
julia> Pop[:,:,2] .= [5 6 7];
julia> ind = findall(x -> x==6 || x==7, Pop[:,:,2])
2-element Vector{CartesianIndex{2}}:
CartesianIndex(1, 2)
CartesianIndex(1, 3)
julia> Pop[ind, 3] .= 8;
julia> Pop[:, :, 3]
1×3 Matrix{Int8}:
3 8 8
You could also write ind == findall(in((6,7)), #view Pop[:,:,2]). You can write ind_bool = (Pop[:,:,2] .== 6) .| (Pop[:,:,2] .== 7) but I'm not sure Pop[ind_bool, 3] .= 8 will work on all versions of Julia.
Another way is just to write an explicit loop. We could loop separately over for i in axes(Pop,1), j in axes(Pop,2) but we can also use these multi-dimensional CartesianIndex things again:
julia> Pop = fill(Int8(3), 1, 3, 4);
julia> Pop[:,:,2] .= [5 6 7];
julia> for i in CartesianIndices(#view Pop[:,:,2])
x = Pop[i,2]
if x==6 | x==7
Pop[i,3] = 8
end
end
julia> Pop[:, :, 3]
1×3 Matrix{Int8}:
3 3 8

Answer 3

Thanks to help from #mcabbott and #Nathan Boyer, I've got a solution that works, even managed to add more conditions and it seems to work. I'll post the mwe solution.
# create new array
Pop = fill(Int8(3), 1, 3, 4)
# change some values
Pop[:,:,2] = [5,6,7]
Pop[:,:,4] = [9,10,9]
# what does it look like
Pop
# code to check condition values
# create temp array to be altered if conditions met
temp = Pop[:,:,3]
# see which indexes meet conditions, in this case
# array "Pop[:,:,2]" contains either 6 or 7 ... and ...
# array "Pop[:,:,4]" contains values >= 10
temp[(Pop[:,:,2] .== 6) .|
(Pop[:,:,2] .== 7) .&
(Pop[:,:,4] .>= 10)] .= 8
# make changes to original array based on temp
Pop[:,:,3] = temp
# check if it did the job correctly
Pop