start index at 1 for Pandas DataFrame

Question

I need the index to start at 1 rather than 0 when writing a Pandas DataFrame to CSV.

Here's an example:

In [1]: import pandas as pd  In [2]: result = pd.DataFrame({'Count': [83, 19, 20]})  In [3]: result.to_csv('result.csv', index_label='Event_id')                                

Which produces the following output:

In [4]: !cat result.csv Event_id,Count 0,83 1,19 2,20 

But my desired output is this:

In [5]: !cat result2.csv Event_id,Count 1,83 2,19 3,20 

I realize that this could be done by adding a sequence of integers shifted by 1 as a column to my data frame, but I'm new to Pandas and I'm wondering if a cleaner way exists.

Answer 1

Index is an object, and default index starts from 0:

>>> result.index Int64Index([0, 1, 2], dtype=int64) 

You can shift this index by 1 with

>>> result.index += 1  >>> result.index Int64Index([1, 2, 3], dtype=int64) 

Answer 2

Just set the index before writing to CSV.

df.index = np.arange(1, len(df)) 

And then write it normally.