根据每一列的值索引行值

Question

I have an 8r x 10c data frame and I want to duplicate the dataframe by dividing the values in each row by the first value in its column (ie 'indexing' each column, with the first value = 100).

So if I start with...

ColA ColB ColC
1000 2000 3000
2000 3000 9000

It would return...

ColA ColB ColC
 100  100  100
 200  150  300

Is there a simple command to do this, or is it some sort of loop?

Answer 1

You could do the following:

>>> df / (df.iloc[0] / 100)
   ColA ColB ColC
0   100  100  100
1   200  150  300

df.iloc[0] selects the first row. Divide it by 100 to get a row of values to adjust each column by. Lastly we divide the entire DataFrame by this new row of values. Division happens along axis 0 by default (ie downwards along each column).

An equivalent operation would be df / df.iloc[0] * 100 .