pandas DataFrame,如何将函数应用于特定列？

Question

我已经阅读了DataFrame.apply的文档

DataFrame.apply(func,axis = 0,broadcast = False,raw = False,reduce = None,args =(),**kwds)沿DataFrame的输入轴应用函数.

那么,如何将函数应用于特定列？

In [1]: import pandas as pd
In [2]: data = {'A': [1, 2, 3], 'B': [4, 5, 6], 'C': [7, 8, 9]}
In [3]: df = pd.DataFrame(data)
In [4]: df
Out[4]: 
   A  B  C
0  1  4  7
1  2  5  8
2  3  6  9
In [5]: def addOne(v):
...:        v += 1
...:        return v
...: 
In [6]: df.apply(addOne, axis=1)
Out[6]: 
   A  B   C
0  2  5   8
1  3  6   9
2  4  7  10

我想将addOne添加到每个值中df['A'],而不是所有列中.我怎么能这样做DataFrame.apply.

感谢帮助!

Answer 1

答案是,

df['A'] = df['A'].map(addOne)

也许你会更好地了解差异的map,applymap,apply.

但如果你坚持使用apply,你可以尝试如下.

def addOne(v):
    v['A'] += 1
    return v

df.apply(addOne, axis=1)

Answer 2

一个简单的方法是:

df['A'] = df['A'].apply(lambda x: x+1)