I want to join these two columns in a new Dataframe like this:

CodePudding user response：

join and explode:

out = (df_id.join(df_cast['Cast'].str.split(',\s*'))
        .explode('Cast')
     )

Or explode and join:

out = df_id.join(df_cast['Cast'].str.split(',\s*').explode('Cast'))