Move columns within Pandas DATA FRAME

Question

I have read data from csv file into a data frame consisting of more than 25000 rows and 15 columns and I need to move all rows (including the left-most -> index) one column to the right, so that I get an empty index and be able to fill it with integers. Names of columns, however, should stay at the same place. So, basically I need to move everything except column names one place to the right.

I tried to reindex it, but got an error:

ValueError: cannot reindex from a duplicate axis

Is there any way to do this?

Answer 1

In pandas you can only create a column to the right, unless you do join between two dataframe. Then you can re-arrange however you like.

import pandas as pd

df = pd.read_csv('data.csv', header=None, names = ['A','B','C'])

print(df)

    A   B   C
0   1   2   3
1   4   5   6
2   7   8   9
3  10  11  12

df['D'] = pd.np.nan # this creates an empty series
                    # and appends to the right

print(df)

    A   B   C   D
0   1   2   3 NaN
1   4   5   6 NaN
2   7   8   9 NaN
3  10  11  12 NaN

df = df[['D','A','B','C']] # rearrange as you like

print(df)

    D   A   B   C
0 NaN   1   2   3
1 NaN   4   5   6
2 NaN   7   8   9
3 NaN  10  11  12