pandas DataFrame，如何将功能应用于特定列? [英] pandas DataFrame, how to apply function to a specific column?

问题描述

我已阅读 DataFrame.apply

DataFrame.apply(func，axis = 0，广播= False，raw = False，reduce = None，args =()，** kwds)¶ 沿DataFrame的输入轴应用功能.

DataFrame.apply(func, axis=0, broadcast=False, raw=False, reduce=None, args=(), **kwds)¶ Applies function along input axis of DataFrame.

那么，如何将函数应用于特定列?

So, How can I apply a function to a specific column?

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

我想为df['A']中的每个值而不是所有列添加一个.我该怎么用DataFrame.apply.

I want to addOne to every value in df['A'], not all columns. How can I do that with DataFrame.apply.

感谢您的帮助！

推荐答案

答案是

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

，也许您会更好地了解区别(map，applymap，apply).

and maybe you would be better to know about the difference of map, applymap, apply.

但是如果您坚持使用apply，则可以尝试以下操作.

but if you insist to use apply, you could try like below.

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

df.apply(addOne, axis=1)

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