I have a layer of polygons, where in some polygons there is missing data (null). I would like to fill these missing attributes by the average attributes in neighboring polygons. Is there a simple way to achieve this?
The simple way to start doing this will be to use the Polygon Neighbors tool to determine the neighbors of each polygon.
There is detailed documentation on how How Polygon Neighbors Works because it is a very flexible tool.
If it does not do what you need then it should be possible to post-process the output using ArcPy cursors to do so.