Попробуйте использовать pd.melt()
, проще:
df.melt('Name',var_name='Dates',value_name='Number')
Name Dates Number
0 andre 22-2019 5
1 Marc 22-2019 12
2 andre 23-2019 3
3 Marc 23-2019 64
Или:
m=df.set_index('Name').stack().reset_index()
m.columns=['Name','Date','Number']
print(m)
Name Date Number
0 andre 22-2019 5
1 andre 23-2019 3
2 Marc 22-2019 12
3 Marc 23-2019 64