Python pandas - pd.melt a dataframe with datetime index results in NaN

Question

I have the following dataframe (sim_2005):

Date         ELEM1 ELEM2 ... ELEM1133
2005-01-01   0.021 2.455 ... 345.2
2005-01-02   0.321 2.331 ... 355.1
...            


        

Answer 1

Assuming Date is the index to your DataFrame, you can get a date column in your melted DataFrame as follows:

sim_2005_melted['Date'] = pd.concat([sim_2005.reset_index().Date 
                                     for _ in range(sim_2005.shape[1])], 
                                    ignore_index=True).values