How to 1D integrate along a path inside mesh

[Emma87 (Emmanuel Yarleque Medina)]

see it:

How to 1d intergrate along x/y direction in 2d mesh

Now I have a mesh Th defined in the square from x = 0 to 1, y = 0 to 1. I solve a PDE on this mesh, getting solution u. Then I want to know the line integral of u along y to get ∫𝑢𝑑𝑦, but I don’t know how to implement