这是什么意思？ xarray 错误：无法处理非唯一的多索引

Question

I am trying to convert a dataframe to xarray. The head is like this:

z   Class    DA       x          y          iline      xline      idz                                                      
2     651   289  1455.0        2.0        0.62239  2345322.0  76720.0
            290  1460.0        0.0        0.46037  2345322.0  76720.0
            291  1465.0        4.0        0.41280  2345322.0  76720.0
            292  1470.0        0.0        0.39540  2345322.0  76720.0
            293  1475.0        2.0        0.61809  2345322.0  76720.0

when I use xr.DataSet.from_dataframe , or df.to_xarray , I got the following error message:

cannot handle a non-unique multi-index!

Anybody know what is going on here?

Answer 1

The multi-index of your data frame has duplicate entries, which xarray cannot unstack into a multi-dimensional array -- the elements of the hypothetical arrays would not have unique values.

You need to remove the duplicated entries in the index first, eg, as described in Remove pandas rows with duplicate indices :

• The simplest choice would be to drop duplicates, eg, df[~df.index.duplicated()]
• You might also use a groupby operation, eg, to compute the mean: df.groupby(level=df.index.names).mean()

Once you've done this, you can safely convert the dataframe into xarray.

Answer 2

In this case df.columns.is_unique would return False . To identify which one is repeating you can see the frequency of each column pair by df.columns.value_counts() . For multiindexing to work it should show 1 for all tuples.

Answer 3

当您通过to_xarray将 csv 转换为 netcdf 时，头部的排列与 cod 中的排列相同很重要，否则会出现error: cannot handle a non-unique multi-index 。