使用日期索引合并pandas数据框

Question

我正在尝试合并两个数据框（我们称它们为df1和df2），这两个数据框的长度不同，都是按照日期来索引的。较长的那个数据框（df1）包含了较短的那个（df2）中所有的日期。我试着用以下命令来合并它们：merged = df2.merge(df1, on='Date')，但是当我这样做时，出现了一些我不理解的错误。

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-47-e8d3e1ec920d> in <module>()
----> 1 merged = df2.merge(df1, on='Date')

/usr/lib/python2.7/dist-packages/pandas/core/frame.pyc in merge(self, right, how, on, left_on, right_on, left_index, right_index, sort, suffixes, copy)
  3630                      left_on=left_on, right_on=right_on,
  3631                      left_index=left_index, right_index=right_index, sort=sort,
-> 3632                      suffixes=suffixes, copy=copy)
  3633 
  3634     #----------------------------------------------------------------------

/usr/lib/python2.7/dist-packages/pandas/tools/merge.pyc in merge(left, right, how, on, left_on, right_on, left_index, right_index, sort, suffixes, copy)
    37                          right_on=right_on, left_index=left_index,
    38                          right_index=right_index, sort=sort, suffixes=suffixes,
---> 39                          copy=copy)
    40     return op.get_result()
    41 if __debug__:

/usr/lib/python2.7/dist-packages/pandas/tools/merge.pyc in __init__(self, left, right, how, on, left_on, right_on, axis, left_index, right_index, sort, suffixes, copy)
    181         (self.left_join_keys,
    182          self.right_join_keys,
--> 183          self.join_names) = self._get_merge_keys()
    184 
    185     def get_result(self):

/usr/lib/python2.7/dist-packages/pandas/tools/merge.pyc in _get_merge_keys(self)
    324                 else:
    325                     if not is_rkey(rk):
--> 326                         right_keys.append(right[rk].values)
    327                         if lk == rk:
    328                             # avoid key upcast in corner case (length-0)

/usr/lib/python2.7/dist-packages/pandas/core/frame.pyc in __getitem__(self, key)
  1656             return self._getitem_multilevel(key)
  1657         else:
-> 1658             return self._getitem_column(key)
  1659 
  1660     def _getitem_column(self, key):

/usr/lib/python2.7/dist-packages/pandas/core/frame.pyc in _getitem_column(self, key)
  1663         # get column
  1664         if self.columns.is_unique:
-> 1665             return self._get_item_cache(key)
  1666 
  1667         # duplicate columns & possible reduce dimensionaility

/usr/lib/python2.7/dist-packages/pandas/core/generic.pyc in _get_item_cache(self, item)
  1003         res = cache.get(item)
  1004         if res is None:
-> 1005             values = self._data.get(item)
  1006             res = self._box_item_values(item, values)
  1007             cache[item] = res

/usr/lib/python2.7/dist-packages/pandas/core/internals.pyc in get(self, item)
  2872                 return self.get_for_nan_indexer(indexer)
  2873 
-> 2874             _, block = self._find_block(item)
  2875             return block.get(item)
  2876         else:

/usr/lib/python2.7/dist-packages/pandas/core/internals.pyc in _find_block(self, item)
  3184 
  3185     def _find_block(self, item):
-> 3186         self._check_have(item)
  3187         for i, block in enumerate(self.blocks):
  3188             if item in block:

/usr/lib/python2.7/dist-packages/pandas/core/internals.pyc in _check_have(self, item)
  3191     def _check_have(self, item):
  3192         if item not in self.items:
-> 3193             raise KeyError('no item named %s' % com.pprint_thing(item))
  3194 
  3195     def reindex_axis(self, new_axis, indexer=None, method=None, axis=0,

KeyError: u'no item named Date'

我还尝试过去掉on='Date'这个部分，因为它们都是按照日期来索引的，但结果似乎还是一样。你觉得我可能哪里出错了呢？

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使用日期索引合并pandas数据框

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