Some math manipulation on the output file before saving to .sdf

[LuWangPhysics]

Hello,
I am focusing on a 2D problem and need to output the electric field ey at a given x=x0 location and sum over y.
In other words, I need sum_i ey(x0,y_i). My needed saving time step is 0.01*femto.

However, in the output file, only the ey over the entire x-y mesh is saved for each snapshot, which requires too much storage memory.

Is it possible to have some level of manipulation on the output file, i.e. performing a sum along a certain dimension for the electric field? If there are other possibilities to output the electric field with very fine time resolution, please also feel free to suggest.

thanks
Lu