Python pandas DataFrame，如何将函数应用于特定列？
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pandas DataFrame, how to apply function to a specific column?
提问by GoingMyWay
I have read the docs of DataFrame.apply
我已经阅读了DataFrame.apply的文档
DataFrame.apply(func, axis=0, broadcast=False, raw=False, reduce=None, args=(), **kwds)? Applies function along input axis of DataFrame.
DataFrame.apply(func,axis=0,broadcast=False,raw=False,reduce=None,args=(),**kwds)？沿 DataFrame 的输入轴应用函数。
So, How can I apply a function to a specific column?
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
I want to addOne to every value in df['A'], not all columns. How can I do that with DataFrame.apply.
我想将 addOne 添加到 中的每个值df['A']，而不是所有列。我怎么能用DataFrame.apply.
Thanks for help!
感谢帮助！
回答by su79eu7k
The answer is,
答案是，
df['A'] = df['A'].map(addOne)
and maybe you would be better to know about the differenceof map, applymap, apply.
也许你会更好地了解的区别的map，applymap，apply。
but if you insist to use apply, you could try like below.
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)
回答by felix_as
One simple way would be:
一种简单的方法是：
df['A'] = df['A'].apply(lambda x: x+1)
