How to write index of dataframe as a dataframe column [duplicate]

Question

How do you write an index of a dataframe to itself?

For Example:

      50       51
   0  326.32   193.1
   1  324.2    192.1
   2  234.2    0
   3  302.1    23

I would like to write a column named index with the index values to the df:

      index     50       51
   0  0         326.32   193.1
   1  1         324.2    192.1
   2  2         234.2    0
   3  3         302.1    23

Answer 1

using df.index

In [94]: df['index'] = df.index

In [95]: df
Out[95]:
       50     51  index
0  326.32  193.1      0
1  324.20  192.1      1
2  234.20    0.0      2
3  302.10   23.0      3

Answer 2

Just:

df['index'] = df.index

where df is your dataframe.

Answer 3

Another way is to use df.reset_index(). But this also resets your index (which is important if your original index was not just 0, 1, 2, 3...)

http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.reset_index.html