Change an element in the last row of a DataFrame

Question

I set up a simple DataFrame in pandas:

a = pandas.DataFrame([[1,2,3], [4,5,6], [7,8,9]], columns=[\'a\',\'b\',\'c\'])
>>> print a
   a  b  c
0  1  2         


        

Answer 1

For pandas 0.22,

a.at[a.index[-1], 'a'] = 77

this is just one of the ways.

Answer 2

Alright I've found a way to solve this problem without chaining, and without worrying about multiple indices.

a.iloc[-1, a.columns.get_loc('a')] = 77
>>> a
   a  b  c
0  1  2  3
1  4  5  6
2 77  8  9

I wasn't able to use iloc before because I couldn't supply the column index as an int, but get_loc solves that problem. Thanks for the helpful comments everyone!

Answer 3

Taking elements from the solutions of @PallavBakshi and @Mike, the following works in Pandas >= 0.19

Just using iloc[-1, 'a] won't work as -1 is not in the index.

a.loc[a.index[-1], 'a']= 4.0