Add range of mulitlevel index in Python

Question

I would like to add a column containing the range of the first level of a multi-level index in Python. For example:

| Index1| Index2| count_of_Index1_Instances |  
---------------------------------------------
|   1   |  20   |           1              |
|       |  40   |           2              |
|       |  10   |           3              |
|   2   |  20   |           1              |

I know thedf.groupby(level=['Index1']).size() command, but this is not what I am looking for. The result in the last column should be a range from 1 to the size of Index-Group1.
Some piece of code would be great!
Thank you!

Is this what you mean.. df.groupby(level=['Index1']).cumcount().add(1)? — Chris Adams
– Chris Adams, Commented Mar 14, 2019 at 17:09

Chris Adams · Accepted Answer · 2019-03-14 17:11:04Z

1

IIUC, use groupby.cumcount and add 1:

df['count_of_Index1_Instances'] = df.groupby(level=['Index1']).cumcount().add(1)

answered Mar 14, 2019 at 17:11

Chris Adams

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1 Comment

Lisa Over a year ago

Perfect! Thanks!

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