python - 如何在Python pandas中进行除法

Question

考虑下面是我的数据框，我想通过将各个标记除以总计来获取百分比来填充“百分比”列。

    Name  Marks
0  Total    100
1  Name1     45
2  Name2     65
3  name3     93
4  name4     89

我写的代码是这样的

for i in range(0,5):
        pcnt=(df['Marks'][i])/(df['Marks'][0])
        df['Percentage']=pcnt*100

但是百分比列只为所有行生成 0。上面的代码只是一个例子，但我的实际数据会产生一些错误，如下所示

Traceback (most recent call last):
  File "C:/Users/USER/.PyCharmCE2017.2/config/scratches/scratch.py", line 24, in <module>
    share=df2['W/E 17/11/2013'][i]/df2['W/E 17/11/2013'][0]
  File "C:\Python27\lib\site-packages\pandas\core\series.py", line 623, in __getitem__
    result = self.index.get_value(self, key)
  File "C:\Python27\lib\site-packages\pandas\core\indexes\base.py", line 2560, in get_value
    tz=getattr(series.dtype, 'tz', None))
  File "pandas/_libs/index.pyx", line 83, in pandas._libs.index.IndexEngine.get_value
  File "pandas/_libs/index.pyx", line 91, in pandas._libs.index.IndexEngine.get_value
  File "pandas/_libs/index.pyx", line 139, in pandas._libs.index.IndexEngine.get_loc
  File "pandas/_libs/hashtable_class_helper.pxi", line 811, in pandas._libs.hashtable.Int64HashTable.get_item
  File "pandas/_libs/hashtable_class_helper.pxi", line 817, in pandas._libs.hashtable.Int64HashTable.get_item
KeyError: 74L

我在这里做错了什么？

Answer 1

我相信你可以使用Series.div按 loc 选择的第一行然后乘以 mul :

s = df['Marks'].div(df.loc[0, 'Marks']).mul(100)
print (s)
0    100.0
1     45.0
2     65.0
3     93.0
4     89.0
Name: Marks, dtype: float64

如果真实数据在第一行没有索引0，则使用通用解决方案 - 按位置选择 iloc与 get_loc对于列标记的位置:

print (df.iloc[0, df.columns.get_loc('Marks')])
100

s = df['Marks'].div(df.iloc[0, df.columns.get_loc('Marks')]).mul(100)