「ValueError：重複した軸からインデックスを再作成できません」というエラーが発生するのはなぜですか？

ここでは、エラーをスローしているコードの部分をポーズしているだけです。ここでは、2つの異なるリストに追加された2つの異なるデータフレームのセットを連結しています。

path1 = '/home/Desktop/computed_2d_blaze/'
path2 = '/home/Desktop/computed_1d/'
path3 = '/home/Desktop/sn_airmass_seeing/'

dir1 = [x for x in os.listdir(path1) if '.ares' in x]
dir2 = [x for x in os.listdir(path2) if '.ares' in x]
dir3 = [x for x in os.listdir(path3) if '.ares' in x]

lst = []
lst1 = []

for file1, file2,file3 in zip(dir1,dir2,dir3):
   df1 = pd.read_table(path1+file1, skiprows=0, usecols=(0,1,2,3,4,8),names=['wave','num','stlines','fwhm','EWs','MeasredWave'],delimiter=r'\s+')
   df2 = pd.read_table(path2+file2, skiprows=0, usecols=(0,1,2,3,4,8),names=['wave','num','stlines','fwhm','EWs','MeasredWave'],delimiter=r'\s+')

   df1 = df1.groupby('wave').mean().reset_index()
   df1 = df1.sort_values('wave').reset_index(drop=True)
   df2 = df2.sort_values('wave').reset_index(drop=True)

   dfs = pd.merge(df1,df2, on='wave', how='inner')
   dfs['delta_ew'] = (dfs.EWs_x - dfs.EWs_y)
   dfs=dfs.filter(items=['wave','delta_ew'])
   lst.append(dfs)

   df3 = pd.read_table(path3+file3, skiprows=0, usecols=(0,1,2),names=['seeing','airmass','snr'],delimiter=r'\s+')
   lst1.append(df3)

[df.set_index('wave', inplace=True) for df in lst]
df=pd.concat(lst,axis=1,join='inner')

x = pd.concat(lst1,axis=1,join='inner')

for z in df.index:
   t = x.loc[0, 'airmass']
   s = df.loc[z, 'delta_ew']
   dfs = pd.concat([s,t],axis=1,names=['delta_ew','airmass'])
   dfs = dfs[np.abs(dfs.delta_ew - dfs.delta_ews.mean()) <= (dfs.delta_ews.mad())]

外れ値がいくつかあるdelta_ewので、新しいデータフレームを作成しようとしているので、それらを削除するためにこれを行っています。しかし、これを実行しようとすると、このエラーが発生しましたValueError: cannot reindex from a duplicate axis。

このエラーを解決する方法がわかりません。どこで間違いを犯しているのか誰か教えてもらえますか？

これが完全なトレースバックです

 Traceback (most recent call last):
  File "/home/gyanender/Desktop/r_values/airmass_vs_ew/delta_ew/for_rvalues.py", line 72, in <module>
    dfs = pd.concat([s,t],axis=1,names=['delta_ew','airmass'])
  File "/home/gyanender/.local/lib/python2.7/site-packages/pandas/core/reshape/concat.py", line 213, in concat
    return op.get_result()
  File "/home/gyanender/.local/lib/python2.7/site-packages/pandas/core/reshape/concat.py", line 385, in get_result
    df = cons(data, index=index)
  File "/home/gyanender/.local/lib/python2.7/site-packages/pandas/core/frame.py", line 330, in __init__
    mgr = self._init_dict(data, index, columns, dtype=dtype)
  File "/home/gyanender/.local/lib/python2.7/site-packages/pandas/core/frame.py", line 461, in _init_dict
    return _arrays_to_mgr(arrays, data_names, index, columns, dtype=dtype)
  File "/home/gyanender/.local/lib/python2.7/site-packages/pandas/core/frame.py", line 6168, in _arrays_to_mgr
    arrays = _homogenize(arrays, index, dtype)
  File "/home/gyanender/.local/lib/python2.7/site-packages/pandas/core/frame.py", line 6465, in _homogenize
    v = v.reindex(index, copy=False)
  File "/home/gyanender/.local/lib/python2.7/site-packages/pandas/core/series.py", line 2681, in reindex
    return super(Series, self).reindex(index=index, **kwargs)
  File "/home/gyanender/.local/lib/python2.7/site-packages/pandas/core/generic.py", line 3023, in reindex
    fill_value, copy).__finalize__(self)
  File "/home/gyanender/.local/lib/python2.7/site-packages/pandas/core/generic.py", line 3041, in _reindex_axes
    copy=copy, allow_dups=False)
  File "/home/gyanender/.local/lib/python2.7/site-packages/pandas/core/generic.py", line 3145, in _reindex_with_indexers
    copy=copy)
  File "/home/gyanender/.local/lib/python2.7/site-packages/pandas/core/internals.py", line 4139, in reindex_indexer
    self.axes[axis]._can_reindex(indexer)
  File "/home/gyanender/.local/lib/python2.7/site-packages/pandas/core/indexes/base.py", line 2944, in _can_reindex
    raise ValueError("cannot reindex from a duplicate axis")
ValueError: cannot reindex from a duplicate axis