Pandas: apply different functions to different columns

Question

When using df.mean() I get a result where the mean for each column is given. Now let\'s say I want the mean of the first column, and the sum of the second. Is t

Answer 1

I think you can use the agg method with a dictionary as the argument. For example:

df = pd.DataFrame({'A': [0, 1, 2], 'B': [3, 4, 5]})

df =
A   B
0   0   3
1   1   4
2   2   5

df.agg({'A': 'mean', 'B': sum})

A     1.0
B    12.0
dtype: float64

Answer 2

Just faced this situation myself and came up with the following:

In [1]: import pandas as pd

In [2]: df = pd.DataFrame([['one', 'two'], ['three', 'four'], ['five', 'six']], 
   ...:                   columns=['A', 'B'])

In [3]: df
Out[3]: 
       A     B
0    one   two
1  three  four
2   five   six

In [4]: converters = {'A': lambda x: x[:1], 'B': lambda x: x.replace('o', '')}

In [5]: new = pd.DataFrame.from_dict({col: series.apply(converters[col]) 
   ...:                               if col in converters else series
   ...:                               for col, series in df.iteritems()})

In [6]: new
Out[6]: 
   A    B
0  o   tw
1  t  fur
2  f  six

Answer 3

You can try a closure:

def multi_func(functions):
    def f(col):
        return functions[col.name](col)
    return f

df = pd.DataFrame(np.random.random((10, 2)), columns=['A', 'B'])
result = df.apply(multi_func({'A': np.mean, 'B': np.sum}))