Apply function on Pandas dataframe

Question

I'm a newbie to pandas dataframe, and I wanted to apply a function to each column so that it computes for each element x, x/max of column.

I referenced this question, but am having trouble accessing the maximum of each column. Thanks in advance Pandas DataFrame: apply function to all columns

Input:

      A  B  C  D
   0  8  3  5  8
   1  9  4  0  4
   2  5  4  3  8
   3  4  8  5  1

Output:

      A     B     C    D
   0  8/9  3/8  5/5  8/8
   1  9/9  4/8  0/5  4/8
   2  5/9  4/8  3/5  8/8
   3  4/9  8/8  5/5  1/8

Would "0.888.." suffice, or do you really need the fraction 8/9? — DSM
– DSM, Commented Dec 18, 2012 at 17:59
Oh yes, 0.888 would be great. It was intended to show the operation. Sorry for the confusion. — msunbot
– msunbot, Commented Dec 18, 2012 at 18:02

DSM · Accepted Answer · 2012-12-18 18:03:13Z

14

Something like this should work:

>>> from pandas import DataFrame
>>> 
>>> df = DataFrame({"A": [8,9,5,4], "B": [3,4,4,8], "C": [5,0,3,5], "D": [8,4,8,1]})
>>> df.max()
A    9
B    8
C    5
D    8
>>> (df * 1.0)/df.max()
          A      B    C      D
0  0.888889  0.375  1.0  1.000
1  1.000000  0.500  0.0  0.500
2  0.555556  0.500  0.6  1.000
3  0.444444  1.000  1.0  0.125

Note that I multiplied df by 1.0 so that it didn't consists of ints anymore (.astype(float) would have worked too) to avoid integer division and a resulting DataFrame full of 0s and 1s.

answered Dec 18, 2012 at 18:03

DSM

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