From 3D to 2D in Python

Question

I would like to have this code:

chains3D = [[] for k in range(colors)]
        def addr(x,y,z): return x + (nx) * (y + (ny) * (z))
        for x in range(nx):
            for y in range(ny):
                for z in range(nz):
                    if (image[x,y,z] == background):
                        chains3D[1].append(addr(x,y,z))
                    else:
                        chains3D[0].append(addr(x,y,z))

in something like this:

chains2D = [[] for k in range(colors)]
        def addr(x,y): return x + (nx) * y 
        for x in range(nx):
            for y in range(ny):
                    if (image[x,y,0] == background):
                        chains2D[1].append(addr(x,y))
                    else:
                        chains2D[0].append(addr(x,y))

Ok I've solved the code issue, but now I've this error:

IndexError                                Traceback (most recent call last)
<ipython-input-5-6a7d44bd72b7> in <module>()
213                         objectBoundaryChain = larBoundaryChain(partial_3,chains2D[1])
214                         b2cells = csrChainToCellList(objectBoundaryChain)
--> 215                         sup_cell_boundary = MKPOLS((V,[FV[f] for f in b2cells]))
216 
217                         # remove the (local) boundary (shared with the piece boundary)     from the quotient cell

/Users/Fabio/larpy/lar.pyc in MKPOLS(model)
101     """
102     V, FV = model
--> 103     pols = [MKPOL([[V[v] for v in f],[range(1,len(f)+1)], None]) for f in FV]
104     return pols
105 

IndexError: list index out of range

I don't know why f is equals to the last number of b2cells, instead of the first, but maybe this is not the real problem that produce this error

Answer 1

It is not entirely clear what you're trying to do and what is not working, but something that seemed weird is that you transformed:

return x + (nx) * (y + (ny) * (z))

into:

return x + (nx) * (y + (ny))

Shouldn't it have been:

return x + (nx) * y

instead? Considering that nz doesn't appear in your 3D version, ny shouldn't appear in the 2D one.