I've got a multidimensional numpy array that I'm trying to stick into a pandas data frame. I'd like to flatten the array, and create a pandas index that reflects the pre-flattened array indices. 

*Note I'm using 3D to keep the example small, but I'd like to generalize to at least 4D*

```
A = np.random.rand(2,3,4)
array([[[ 0.43793885,  0.40078139,  0.48078691,  0.05334248],
    [ 0.76331509,  0.82514441,  0.86169078,  0.86496111],
    [ 0.75572665,  0.80860943,  0.79995337,  0.63123724]],

   [[ 0.20648946,  0.57042315,  0.71777265,  0.34155005],
    [ 0.30843717,  0.39381407,  0.12623462,  0.93481552],
    [ 0.3267771 ,  0.64097038,  0.30405215,  0.57726629]]])

df = pd.DataFrame(A.flatten())

```

I'm trying to generate x/y/z columns like this:

```
           A  z  y  x
0   0.437939  0  0  0
1   0.400781  0  0  1
2   0.480787  0  0  2
3   0.053342  0  0  3
4   0.763315  0  1  0
5   0.825144  0  1  1
6   0.861691  0  1  2
7   0.864961  0  1  3
...
21  0.640970  1  2  1
22  0.304052  1  2  2
23  0.577266  1  2  3

```

I've tried setting this up using `np.meshgrid` but I'm going wrong somewhere:

```
dimnames = ['z', 'y', 'x']
ranges   = [ np.arange(x) for x in A.shape ]
ix       = [ x.flatten()  for x in np.meshgrid(*ranges) ]
for name, col in zip(dimnames, ix):
    df[name] = col
df = df.set_index(dimnames).squeeze()

```

This result looks somewhat sensible, but the indices are wrong:

```
df
z  y  x
0  0  0    0.437939
      1    0.400781
      2    0.480787
      3    0.053342
1  0  0    0.763315
      1    0.825144
      2    0.861691
      3    0.864961
0  1  0    0.755727
      1    0.808609
      2    0.799953
      3    0.631237
1  1  0    0.206489
      1    0.570423
      2    0.717773
      3    0.341550
0  2  0    0.308437
      1    0.393814
      2    0.126235
      3    0.934816
1  2  0    0.326777
      1    0.640970
      2    0.304052
      3    0.577266

print A[0,1,0]
0.76331508999999997

print print df.loc[0,1,0]
0.75572665000000006

```

How can I create the index columns to reflect the shape of `A`?