Pandas divide one row by another and output to another row in the same dataframe

Question

For a Dataframe such as:

      dt
                COL000  COL001
      STK_ID                
      Rowname1  2  2
      Rowname2  1  4
      Rowname3  1  1

What's the easiest way to append to the same data frame the result of dividing Row1 by Row2? i.e. the desired outcome is:

                COL000  COL001
      STK_ID                
      Rowname1  2  2
      Rowname2  1  4
      Rowname3  1  1
      Newrow    2  0.5

Sorry if this is a simple question, I'm slowly getting to grips with pandas from an R background.

Thanks in advance!!!

Answer 1

The code below will create a new row with index d which is formed from dividing rows a and b.

import pandas as pd


df = pd.DataFrame(data={'x':[1,2,3], 'y':[4,5,6]}, index=['a', 'b', 'c'])

df.loc['d'] = df.loc['a'] / df.loc['b']

print(df)
#      x    y
# a  1.0  4.0
# b  2.0  5.0
# c  3.0  6.0
# d  0.5  0.8

Answer 2

in order to access the first two rows without caring about the index, you can use:

df.loc['newrow'] = df.iloc[0] / df.iloc[1]

then just follow @Ffisegydd's solution...

in addition, if you want to append multiple rows, use the pd.DataFrame.append function.