[英]Create column based on row data when column doesn't exist or column is NaN in pandas
[英]Why does pandas give NaN for column values when aggregating a column that doesn't exist?
我想在下面的DataFrame中按字母數字求和:
In [10]: df
Out[10]:
letter number
0 A 1
1 A 2
2 B 3
3 B 4
4 C 5
5 C 6
[6 rows x 2 columns]
這很容易實現:
In [11]: df.groupby('letter')[['number']].sum()
Out[11]:
number
letter
A 3
B 7
C 11
[3 rows x 1 columns]
但如果我拼錯我的專欄,我會得到NaN
值:
In [12]: df.groupby('letter')[['numberrrrr']].sum()
Out[12]:
numberrrrr
letter
A NaN
B NaN
C NaN
[3 rows x 1 columns]
這導致我們的團隊非常追逐確定bug的位置。 相反,我們想要一個錯誤陳述,如:
In [13]: df.groupby('letter')['numberrrrr'].sum()
---------------------------------------------------------------------------
KeyError Traceback (most recent call last)
<ipython-input-13-8ebcdeee8710> in <module>()
----> 1 df.groupby('letter')['numberrrrr'].sum()
/usr/local/Anaconda/lib/python2.7/site-packages/pandas/core/groupby.pyc in __getitem__(self, key)
2475 else:
2476 if key not in self.obj: # pragma: no cover
-> 2477 raise KeyError(str(key))
2478 # kind of a kludge
2479 return SeriesGroupBy(self.obj[key], selection=key,
KeyError: 'numberrrrr'
是否有任何特殊原因,當請求的列丟失時,從聚合返回DataFrame不會導致錯誤?
這是關於pandas 0.13.1。
這在master / 0.14.0(本周結束)中修復; 如果您想嘗試,rc1就在這里
In [7]: df.groupby('letter')[['number']].sum()
Out[7]:
number
letter
A 3
B 7
C 11
In [8]: df.groupby('letter')[['numberrrr']].sum()
KeyError: "Columns not found: 'numberrrr'"
In [9]: pd.__version__
Out[9]: '0.14.0rc1-43-g0dec048'
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