Concat two datetime indexed Dataframes-CodePudding

I am having a problem concating two Dataframes without loosing the date time index.

df1:

DateTime             Open     High     Low      Close              
2022-09-22 09:19:00  143.562  143.619  143.227  143.246

df2:

DateTime             Open     High     Low      Close              
2022-09-22 09:20:00  143.660  143.702  143.367  143.355

I am trying to concat with following code:

combined_data = pd.concat([previous_df, df_test], axis=0)

when I try and use concat I get following output:

    Unnamed: 0  DateTime    Open    High    Low Close
    1   1   2022-09-22 09:19:00 NaN 143.562 143.619 143.227 143.246
    2   2022-09-22 09:20:00 NaN NaN 143.098 143.098 142.683 142.698

So now every single Datetime index is created as a new index

I have also tried using join = inner/outer with the same results. Using ignore_index = true/false has the same results

EDIT TO QUESTION:

I found out that the problem exists because df1 is loaded from a csv and either while saving to the csv or loading from csv the index gets lost.

The question now is only how I can save and load the index correctly from a csv.

code for saving to csv:

df.to_csv('datatest.csv')

code for loading from csv:

previous_df = pd.read_csv('datatest.csv')

combined_data = pd.concat([previous_df, df_test], axis=0)

combined_data

CodePudding user response：

Problem arose from reading the csv. Csv did not save index correctly and renamed it to unnamed which is why the two df were not able to concat correctly