Row-wise operation using `map`?

[contradict]

How about mapslices

julia> aa = [1. 2. 3.; 4. 5. 6.]
2×3 Matrix{Float64}:
 1.0  2.0  3.0
 4.0  5.0  6.0

julia> mapslices(sum, aa; dims=2)
2×1 Matrix{Float64}:
  6.0
 15.0