pandas.DataFrame.apply 基本用法

pandas.DataFrame.apply() 方法用于将给定函数应用于整个 DataFrame —例如，计算给定 DataFrame 的每个条目的平方根或者对 DataFrame 的每一行求和以返回 Series。

以下是此功能的基本使用示例：

# create a random DataFrame with 7 rows and 2 columns
df = pd.DataFrame(np.random.randint(0,100,size = (7,2)), 
                  columns = ['fst','snd'])

>>> df
   fst  snd
0   40   94
1   58   93
2   95   95
3   88   40
4   25   27
5   62   64
6   18   92

# apply the square root function to each column:
# (this returns a DataFrame where each entry is the sqrt of the entry in df;
# setting axis=0 or axis=1 doesn't make a difference)
>>> df.apply(np.sqrt)
        fst       snd
0  6.324555  9.695360
1  7.615773  9.643651
2  9.746794  9.746794
3  9.380832  6.324555
4  5.000000  5.196152
5  7.874008  8.000000
6  4.242641  9.591663

# sum across the row (axis parameter now makes a difference):
>>> df.apply(np.sum, axis=1)
0    134
1    151
2    190
3    128
4     52
5    126
6    110
dtype: int64

>>> df.apply(np.sum)
fst    386
snd    505
dtype: int64