Pandas json_normalize会产生令人困惑的`KeyError`消息？

Question

我正在尝试将嵌套的JSON转换为Pandas数据帧.我一直在json_normalize成功使用,直到遇到某个JSON.我已经制作了一个较小的版本来重现问题.

from pandas.io.json import json_normalize

json=[{"events": [{"schedule": {"date": "2015-08-27",
     "location": {"building": "BDC", "floor": 5},
     "ID": 815},
    "group": "A"},
   {"schedule": {"date": "2015-08-27",
     "location": {"building": "BDC", "floor": 5},
 "ID": 816},
"group": "A"}]}]

然后我跑:

json_normalize(json[0],'events',[['schedule','date'],['schedule','location','building'],['schedule','location','floor']])

期待看到这样的事情:

ID      group   schedule.date   schedule.location.building schedule.location.floor  
'815'   'A'     '2015-08-27'            'BDC'                       5
'816'   'A'     '2015-08-27'            'BDC'                       5

但相反,我得到这个错误:

In [2]: json_normalize(json[0],'events',[['schedule','date'],['schedule','location','building'],['schedule','location','floor']])
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-2-b588a9e3ef1d> in <module>()
----> 1 json_normalize(json[0],'events',[['schedule','date'],['schedule','location','building'],['schedule','location','floor']])

/Users/logan/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/io/json.pyc in json_normalize(data, record_path, meta, meta_prefix, record_prefix)
    739                 records.extend(recs)
    740
--> 741     _recursive_extract(data, record_path, {}, level=0)
    742
    743     result = DataFrame(records)

/Users/logan/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/io/json.pyc in _recursive_extract(data, path, seen_meta, level)
    734                         meta_val = seen_meta[key]
    735                     else:
--> 736                         meta_val = _pull_field(obj, val[level:])
    737                     meta_vals[key].append(meta_val)
    738

/Users/logan/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/pandas/io/json.pyc in _pull_field(js, spec)
    674         if isinstance(spec, list):
    675             for field in spec:
--> 676                 result = result[field]
    677         else:
    678             result = result[spec]

KeyError: 'schedule'

Answer 1

在这种情况下，我想你只需使用这个：

In [57]: json_normalize(data[0]['events'])
Out[57]: 
  group  schedule.ID schedule.date schedule.location.building  \
0     A          815    2015-08-27                        BDC   
1     A          816    2015-08-27                        BDC   

   schedule.location.floor  
0                        5  
1                        5  

路径meta( [['schedule','date']...]) 用于指定与记录处于同一嵌套级别的数据，即与“事件”处于同一级别。它看起来并不能json_normalize很好地处理带有嵌套列表的字典，因此如果您的实际数据要复杂得多，您可能需要进行一些手动重塑。