Question

我一直在数据框架上使用apply方法来创建新列。所以，如果我有一个看起来像这样的df：

stdf.columns
Index(['Username', 'First Name', 'Last Name', 'Class', 'Screens Typed','Time Spent', 'Avg Speed', 'Avg Acc'],  dtype='object')

我正在使用这样的语法来创建新列

stdf['uid'] = stdf['Username'].apply(lambda x: x[0:6]) + "-" + stdf['First Name'] + "-" + stdf['Last Name']

今天，当使用相同的方法创建新列时，我得到了新列名称

的关键词

stdf['truSpeed'] = stdf['nSpeed'].apply(lambda x: x * .1 * stdf["truAcc"])

是的，＆＃39; nSpeed＆＃39;和＆＃39; truAcc＆＃39;以列的形式存在。

Index(['Username', 'First Name', 'Last Name', 'Class', 'Screens Typed', 'Time Spent', 'Avg Speed', 'Avg Acc', 'truTime', 'uid', 'truAcc',

＆＃39; nSpeed＆＃39;]，dtype =＆＃39; object＆＃39;）

keyerror指向＆＃39; truSpeed标识符。所以我的问题是为什么熊猫现在告诉我，当我在过去创建新专栏的时候尝试创建一个新专栏时，我有一个关键错误？

我必须看到其他一些错误。

这里几乎完全追溯

KeyError                                  Traceback (most recent call last)
/home/david/dev/msc/lib/python3.5/site-packages/pandas/indexes/base.py in get_loc(self, key, method, tolerance)
   2133             try:
-> 2134                 return self._engine.get_loc(key)
   2135             except KeyError:

pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4433)()

pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4279)()

pandas/src/hashtable_class_helper.pxi in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:13742)()

pandas/src/hashtable_class_helper.pxi in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:13696)()

KeyError: 'truSpeed'

During handling of the above exception, another exception occurred:

KeyError                                  Traceback (most recent call last)
/home/david/dev/msc/lib/python3.5/site-packages/pandas/core/internals.py in set(self, item, value, check)
   3667         try:
-> 3668             loc = self.items.get_loc(item)
   3669         except KeyError:

/home/david/dev/msc/lib/python3.5/site-packages/pandas/indexes/base.py in get_loc(self, key, method, tolerance)
   2135             except KeyError:
-> 2136                 return self._engine.get_loc(self._maybe_cast_indexer(key))
   2137 

pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4433)()

pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4279)()

pandas/src/hashtable_class_helper.pxi in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:13742)()

pandas/src/hashtable_class_helper.pxi in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:13696)()

KeyError: 'truSpeed'

During handling of the above exception, another exception occurred:

ValueError                                Traceback (most recent call last)
<ipython-input-18-35d20ff4edf0> in <module>()
      4 stdf['nSpeed'] = stdf['Avg Speed'].apply(lambda x: int(x.split(" ")[0]))
      5 print(stdf.columns)
----> 6 stdf['truSpeed'] = stdf['nSpeed'].apply(lambda x: x * .1 * stdf["truAcc"])
      7 # stdf['truSpeed']
      8 # print(stdf.columns)

/home/david/dev/msc/lib/python3.5/site-packages/pandas/core/frame.py in __setitem__(self, key, value)
   2417         else:
   2418             # set column
-> 2419             self._set_item(key, value)
   2420 
   2421     def _setitem_slice(self, key, value):

/home/david/dev/msc/lib/python3.5/site-packages/pandas/core/frame.py in _set_item(self, key, value)
   2484         self._ensure_valid_index(value)
   2485         value = self._sanitize_column(key, value)
-> 2486         NDFrame._set_item(self, key, value)
   2487 
   2488         # check if we are modifying a copy

/home/david/dev/msc/lib/python3.5/site-packages/pandas/core/generic.py in _set_item(self, key, value)
   1498 
   1499     def _set_item(self, key, value):
-> 1500         self._data.set(key, value)
   1501         self._clear_item_cache()
   1502 

/home/david/dev/msc/lib/python3.5/site-packages/pandas/core/internals.py in set(self, item, value, check)
   3669         except KeyError:
   3670             # This item wasn't present, just insert at end
-> 3671             self.insert(len(self.items), item, value)
   3672             return
   3673 

/home/david/dev/msc/lib/python3.5/site-packages/pandas/core/internals.py in insert(self, loc, item, value, allow_duplicates)
   3770 
   3771         block = make_block(values=value, ndim=self.ndim,
-> 3772                            placement=slice(loc, loc + 1))
   3773 
   3774         for blkno, count in _fast_count_smallints(self._blknos[loc:]):

/home/david/dev/msc/lib/python3.5/site-packages/pandas/core/internals.py in make_block(values, placement, klass, ndim, dtype, fastpath)
   2683                      placement=placement, dtype=dtype)
   2684 
-> 2685     return klass(values, ndim=ndim, fastpath=fastpath, placement=placement)
   2686 
   2687 # TODO: flexible with index=None and/or items=None

/home/david/dev/msc/lib/python3.5/site-packages/pandas/core/internals.py in __init__(self, values, placement, ndim, fastpath)
    107             raise ValueError('Wrong number of items passed %d, placement '
    108                              'implies %d' % (len(self.values),
--> 109                                              len(self.mgr_locs)))
    110 
    111     @property

ValueError: Wrong number of items passed 58, placement implies 1

Answer 1

stdf['truSpeed'] = stdf['nSpeed'].apply(lambda x: x * .1 * stdf["truAcc"])

应该是

stdf['truSpeed'] = stdf.eval('nSpeed * truAcc * .1')

或者

stdf['truSpeed'] = stdf['nSpeed'] * stdf['truAcc'] * .1

或者

的缓慢方式

stdf['truSpeed'] = stdf.apply(lambda x: x['nSpeed'] * x['truAcc'] * .1, axis=1)

Answer 2

感谢piRSquared，语法更简单。正如评论中所提到的，df.eval语法是新的，它起作用。但是，似乎适合“＃39; excel电子表格使用的范例是第三种语法

stdf['truSpeed'] = stdf['nSpeed'] * stdf['truAcc'] * .1

我认为最初生成的keyerror必定是由于使用标识符＆＃39; truSpeed＆＃39;而导致的其他一些错误。只是找到在数据框中创建新列。

python 3，pandas和创建新列失败了keyerror

2 个答案: