Convert pandas dataframe to NumPy array

How do I convert a pandas dataframe into a NumPy array?

DataFrame:

import numpy as npimport pandas as pdindex = [1, 2, 3, 4, 5, 6, 7]a = [np.nan, np.nan, np.nan, 0.1, 0.1, 0.1, 0.1]b = [0.2, np.nan, 0.2, 0.2, 0.2, np.nan, np.nan]c = [np.nan, 0.5, 0.5, np.nan, 0.5, 0.5, np.nan]df = pd.DataFrame({'A': a, 'B': b, 'C': c}, index=index)df = df.rename_axis('ID')

gives

      A    B    CID                                 1   NaN  0.2  NaN2   NaN  NaN  0.53   NaN  0.2  0.54   0.1  0.2  NaN5   0.1  0.2  0.56   0.1  NaN  0.57   0.1  NaN  NaN

I would like to convert this to a NumPy array, like so:

array([[ nan,  0.2,  nan],       [ nan,  nan,  0.5],       [ nan,  0.2,  0.5],       [ 0.1,  0.2,  nan],       [ 0.1,  0.2,  0.5],       [ 0.1,  nan,  0.5],       [ 0.1,  nan,  nan]])

Also, is it possible to preserve the dtypes, like this?

array([[ 1, nan,  0.2,  nan],       [ 2, nan,  nan,  0.5],       [ 3, nan,  0.2,  0.5],       [ 4, 0.1,  0.2,  nan],       [ 5, 0.1,  0.2,  0.5],       [ 6, 0.1,  nan,  0.5],       [ 7, 0.1,  nan,  nan]],     dtype=[('ID', '<i4'), ('A', '<f8'), ('B', '<f8'), ('B', '<f8')])