使用两个标头熊猫访问熊猫数据框列

I created a dataframe using groupby and pd.cut to calculate the mean, std and number of elements inside a bin. I used the agg()and this is the command I used:

df_bin=df.groupby(pd.cut(df.In_X, ranges,include_lowest=True)).agg(['mean', 'std','size'])

df_bin看起来像这样:

                 X                  Y
                 mean   std size   mean         std  size
In_X                    
(10.424, 10.43] 10.425  NaN  1      0.003786    NaN   1
(10.43, 10.435] 10.4    NaN  0      NaN         NaN   0

I want to create an array with the values of the mean for the first header X. If I didn't have the two header level, I would use something like:

mean=np.array(df_bin['mean'])

但是如何使用两个标头呢?