Adjust Index Numbers

Hey guys! I have following question/problem!
On one hand i have a couple of closed polylines (BORDERS) and on the other i have a the same amount of polylines (BUILDINGS) within this border lines.
Now i want to calculate the area-difference of each BORDER AREA (BORDER minus associated BUILDING).
But therefore BORDER and BUILDING must have the same position/index in their list.
For example in my case BORDER = index 15 and BUILDING = index 36.
How can i adjust the indices? (14.2 KB)
180305_Schwarzplan Grundgrenzen.3dm (1.4 MB)

Use Curve Nearest Object (CrvNear) component

The area component also computes a centroid. The building´s centroid will nearly always be closest to the centroid of the corresponding plot.
The buildings centroid will always be the only centroid within the plot outline. Attached is a quick suggestion for how it can be done.

Plot building (15.4 KB)

thank you! works perfect!