I tried to search for solution, but seems this problem is quite difficult, and there might not be a good solution.

I want to calculate plastic resistance of cross section, to do it, I need to divide cross section into two equal halves by area, afterwards determine distance between centers of these areas.

Currently best approximation, I could figure out, would be to divide the cross section in 1mm heigh sections, then add each of them together till I reach half of the area. That would determine aproximate axis where the division should be.

I’m worried, that might be too resource intensive to do at once for ~15’000 cross sections.
Other option was doing it by mathematical formulas, but that would work only for specific cross sections, I’d love to see, if there was a possibility of doing it graphically.

You can use the evolutionary solver Galapagos that comes with Grasshopper to attack these kind of tasks. Be warned though, there might not always be a situation where the areas of both cross sections are exactly equal.

I went down the Anemone route - it moves the cutting line succesively up/down depending on which half is bigger. And stops when all the halves are better than a given difference in area

If you have 10-100k cross sections than you need fast code to do the job. At the same time you have to decide what precision/tolerance is acceptable for your solution. I attached multitask solution that is based on principle of binary search algorithm. It process 1000 of cross sections with tolerance 0.001 in 7 seconds. Speed of execution also depends on number of cores you have installed on PC …