Convert columns to rows by index value with Pandas [duplicate]

Question

I have a pandas dataframe structured like this:

Name	Identifier	Tags_0_Value	Tags_1_Value	Tags_2_Value	Tags_3_Value	Tags_4_Value	Tags_5_Value	Tags_6_Value
Bottle Nose Well	1345		A- Groundwater Aquifer	WL - Water Level Network	104 - Area Wide Map	110 - Area Network	114 - Area Wide Monitoring
BMOs Adventure	3745	A - Groundwater Aquifer	HR - Domestic Wells	15 - Baylor County Well Survey	20- Data collection	3 - Water Level Measurable	6 - Onsite	9 - Water Quality

but I want to collapse the columns starting with "Tags" into a single column and append every value to a row indexed by the Name/Identifier, like this:

Name	Identifier	Tags
Bottle Nose Well	1345	A- Groundwater Aquifer
Bottle Nose Well	1345	WL - Water Level Network
Bottle Nose Well	1345	104 - Area Wide Map
Bottle Nose Well	1345	110 - Area Network
Bottle Nose Well	1345	114 - Area Wide Monitoring
BMOs Adventure	3745	A - Groundwater Aquifer
BMOs Adventure	3745	HR - Domestic Wells
BMOs Adventure	3745	15 - Baylor County Well Survey
BMOs Adventure	3745	20- Data collection
BMOs Adventure	3745	3 - Water Level Measurable
BMOs Adventure	3745	6 - Onsite
BMOs Adventure	3745	9 - Water Quality

I've tried the transpose and pivot functions in Pandas, but already know that's not I need.

Answer 1

One way is to set_index + stack:

out = df.set_index(['Name','Identifier']).stack().droplevel(-1).reset_index(name='Tags')

Output:

                Name  Identifier                            Tags
0   Bottle Nose Well        1345          A- Groundwater Aquifer
1   Bottle Nose Well        1345        WL - Water Level Network
2   Bottle Nose Well        1345             104 - Area Wide Map
3   Bottle Nose Well        1345              110 - Area Network
4   Bottle Nose Well        1345      114 - Area Wide Monitoring
5     BMOs Adventure        3745         A - Groundwater Aquifer
6     BMOs Adventure        3745             HR - Domestic Wells
7     BMOs Adventure        3745  15 - Baylor County Well Survey
8     BMOs Adventure        3745             20- Data collection
9     BMOs Adventure        3745      3 - Water Level Measurable
10    BMOs Adventure        3745                      6 - Onsite
11    BMOs Adventure        3745               9 - Water Quality