pandas DataFrame, how to apply function to a specific column?

Question

I have read the docs of DataFrame.apply

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

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 

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

Thanks for help!

Answer 1

The answer is,

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

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

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)