compare does not work for object arrays

[gdementen]

When it contains non numeric data (e.g. strings), the maxdiff is 'nan' and thus, you get no colors.

Worse yet, when it does not contain strings but contains zeros it crashes with ZeroDivisionError because np.seterr(divide='ignore', invalid='ignore') has no effect for object arrays. In effect in that case a / b is mostly equal to calling __truediv__ on each cell and this raises ZeroDivisionError: division by zero