python - Pandas multiindex and pytables... separate indexes or one concatenated index? -

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what structure of pandas multiindex on hdf5 when data frame saved hdf5 through pytables? each of parts separate index or there 1 concatenated index?

it stored df.reset_index(), except index columns automatically data columns (meaning can select them).

in [1]: df = dataframe({'a' : np.random.randn(9)},index=pd.multiindex.from_product([range(3),list('abc')],names=['first','second']))  in [2]: df out[2]:                       first second           0          -1.249058       b      -0.674645       c      -0.000458 1           0.455390       b      -1.693221       c       1.245806 2           0.337478       b       0.672525       c       0.160914  in [3]: store = pd.hdfstore('test.h5',mode='w')  in [4]: store.append('df',df)  in [5]: store            out[5]:  <class 'pandas.io.pytables.hdfstore'> file path: test.h5 /df            frame_table  (typ->appendable_multi,nrows->9,ncols->3,indexers->[index],dc->[second,first])

here's actual structure looks like.

in [7]: store.get_storer('df').table out[7]:  /df/table (table(9,)) ''   description := {   "index": int64col(shape=(), dflt=0, pos=0),   "values_block_0": float64col(shape=(1,), dflt=0.0, pos=1),   "second": stringcol(itemsize=1, shape=(), dflt='', pos=2),   "first": int64col(shape=(), dflt=0, pos=3)}   byteorder := 'little'   chunkshape := (2621,)   autoindex := true   colindexes := {     "index": index(6, medium, shuffle, zlib(1)).is_csi=false,     "second": index(6, medium, shuffle, zlib(1)).is_csi=false,     "first": index(6, medium, shuffle, zlib(1)).is_csi=false}

select levels name

in [9]: store.select('df',where='second="b"') out[9]:                       first second           0     b      -0.674645 1     b      -1.693221 2     b       0.672525  in [10]: store.select('df',where='second="b" & first=2') out[10]:                       first second           2     b       0.672525

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